JPH053295Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an injection molding machine related to a molding technique for a high-viscosity molding material.

[Conventional technology]

In an injection molding machine for high viscosity molding materials such as rubber materials, after the charge operation, a "suckback operation" is performed for the purpose of removing the internal pressure of the molding material replenished into the heating cylinder.

To explain this with reference to FIG. 2, 1 is a heating cylinder, 4 is an injection screw inserted into the heating cylinder 1, and this injection screw 4 is moved forward in the axial direction by a hydraulic cylinder 5 in the same way as a normal plunger. Then, the fluidized molding material in the heating cylinder 1 is injected from the nozzle 2 into the cavity 19 of the mold 18, and after holding pressure for a certain period of time, it is rotated by a hydraulic motor (not shown) to fill the supply port 3. A fixed amount of molding material is replenished (charged) into the heating cylinder 1. Heating tube 1
As the molding material is supplied into the interior, the injection screw 4 and the hydraulic cylinder 5 are gradually pushed back to the rear by the reaction force, but at this time, a part of the hydraulic circuit (not shown) connected to the hydraulic cylinder 5 By the action of the pressure control valve, an appropriate internal pressure is applied to the molding material replenished into the heating cylinder 1. This application of internal pressure during the charging operation has the effect of improving the kneading efficiency due to the rotation of the injection screw 4 and preventing air from entering the molding material as much as possible, but after the charging is completed,
When opening the mold 18 and taking out the product, if the internal pressure is not removed, part of the molding material will flow out from the nozzle 2 into the mold 18, causing molding defects. Therefore, after charging, the injection screw 4 is moved back a little further from the position at the completion of charging to remove the internal pressure of the material, a so-called back-back operation. Figure 3 shows the relationship between the stroke operation of the injection screw 4 and time, with t ₁ being the injection operation, t ₂ being the holding pressure, t ₃ being the retracting operation during charging, and t ₄ being the back-up operation. Do the following.

Conventionally, the backward movement of the injection screw 4 during this backward movement is controlled by a control device (not shown) that determines whether or not the stroke value detected by the stroke sensor 6 matches a preset stroke value. is being carried out.

[Problem that the invention attempts to solve]

However, in the conventional control system described above, the stroke value of the backward motion that is set in advance must be determined through repeated trial and error for each molding material and each lot. Although it is not known to what extent the internal pressure of the molding material has been removed, the current method is to experimentally find and use a stroke value that almost eliminates forming defects, which is a very complicated process.
In addition, even if the molding material and lot are the same, slight changes in conditions such as the degree of kneading and temperature can cause
The internal pressure of the material often differs depending on the molding cycle,
Since the stroke value is set fixedly, it is currently not possible to deal with variations in internal pressure, and there is still the possibility of material flowing out.

In view of the above-mentioned problems, the present invention attempts to solve the problems by using the desired value of the material internal pressure itself as a control factor.

[Means for solving problems]

The injection molding machine according to the present invention includes a heating cylinder equipped with an injection screw that rotates and reciprocates in the axial direction on the inner periphery, and a pressure sensor that detects the internal pressure of the molding material charged into the heating cylinder. , a drive system for smoothly operating the injection screw,
The configuration is such that feedback control is performed based on the value detected by the pressure sensor.

[Effect]

That is, in the above configuration, the amount of retraction of the injection screw during backback is not fixedly set, but the internal pressure of the molding material in the heating cylinder after the charge operation detected by the pressure sensor is zero or The amount of retraction of the injection screw is controlled so that it is below a certain threshold.

〔Example〕

Next, the injection molding machine of the present invention will be explained in more detail based on an illustrated embodiment.

In FIG. 1, as in FIG. 2 described above, numeral 1 is a heating cylinder, 2 is a nozzle that connects to a sprue of a mold (not shown), 3 is a material supply port, 4 is an injection screw, and 5 is a A hydraulic cylinder 6 that reciprocates the screw 4 in the axial direction is a stroke sensor that detects the position (stroke amount) of the injection screw 4. There is a pressure between the hydraulic cylinder 5, the hydraulic source 7, and the hydraulic tank 8 in the hydraulic circuit that constitutes the drive system of the injection molding machine, which has the effect of generating internal pressure in the molding material in the heating cylinder 1 during the charging operation. counterbalance valve 9 as a control valve;
A three-position solenoid valve 10 for controlling the reciprocation of the hydraulic cylinder 5 and the injection screw 4 is also interposed. This solenoid valve 10
When is switched from the illustrated position to the 10a position, the injection screw 4 moves forward to perform an injection operation, and when switched to the 10c position, the injection screw 4 moves backward.
A pressure sensor 11 is installed in the heating cylinder 1 facing the inner peripheral space 1a near the tip of the heating cylinder 1, where the molding material taken in from the supply port 3 is sent and stored by the rotation of the injection screw 4. It is provided. 12
is a control device comprising an input device 13, a setting device 14, a microprocessor 15, a random access memory 16, an output device 17, and the like. Detection signals from the stroke sensor 6 and pressure sensor 11 are input to an input device 13. Furthermore, data necessary for preset control is written in the random access memory 16. The microprocessor 15 performs arithmetic processing based on this information, and issues operation commands from the output device 17 to the three-position switching solenoid valve 10, etc., thereby performing feedback control. The detection signal input from the stroke sensor 6 that detects the position of the injection screw is used as a control factor to control the injection speed of the molding material into the mold and the fixed amount replenishment operation of the molding material during charging. It is what it is. Also,
The detection signal from the pressure sensor 11 is a control factor for controlling the backward stroke amount of the injection screw 4 during the back-back operation. That is, the detection signal from the pressure sensor 11 is a control factor for controlling the backward stroke amount of the injection screw 4 during the back-back operation. The injection screw 4 is designed to perform a backward movement until the internal pressure of the material becomes zero or below a certain preset threshold value.

In this embodiment, a hydraulic circuit is used as the drive system for the injection screw 4, but similar control can also be achieved by using, for example, an AC servo motor as the drive system.

[Effect of idea]

As explained above, in the injection molding machine of the present invention, the backward stroke of the injection screw during back-back after charging is controlled so that the internal pressure of the molding material in the heating cylinder is zero or below a certain value. Therefore, regardless of variations in the conditions for each molding material, material lot, or molding cycle, the internal pressure of the material after charging is controlled to an appropriate value, so the material is stable when the product is removed from the mold. This eliminates leakage accidents and prevents molding defects, and also eliminates the difficult work of finding and setting the injection screw's backward stroke value for back-to-back operation through trial and error. Therefore, it is possible to reduce quality control items (molding conditions), and the practical effect is extremely large.

[Brief description of the drawings]

Fig. 1 is a structural explanatory diagram schematically showing an embodiment of the injection molding machine of the present invention, Fig. 2 is a sectional view of main parts schematically showing a conventional injection molding machine, and Fig. 3 is an operating line of the injection screw. It is a diagram. 1... Heating cylinder, 2... Nozzle, 3... Supply port,
4...Injection screw, 5...Hydraulic cylinder, 6...
...Stroke sensor, 7...Hydraulic pressure source, 8...Hydraulic tank, 9...Counter balance valve, 10
... 3-position switching solenoid valve, 11 ... pressure sensor, 12 ... control device, 13 ... input device,
14... Setting device, 15... Microprocessor, 16... Random access memory, 17...
Output device.

Claims (1)

[Scope of utility model registration request] A pressure sensor 11 for detecting the internal pressure of the molding material charged into the heating cylinder 1 is attached to a heating cylinder 1 equipped with an injection screw 4 that rotates and reciprocates in the axial direction on the inner periphery. The drive system that operates the pressure sensor 1
An injection molding machine characterized by performing feedback control based on the detected value according to No. 1.