JPH01290408A - Method and apparatus for controlling feeding of raw material in vent type injection molder - Google Patents

Abstract

PURPOSE:To prevent venting up from occurring during metering process and realize stable injection molding by a method wherein the rotational frequency of a screw feeder is changed so as to successively decrease at the pre-set position of the stroke of a main screw with the approach of the position of the stroke of the main screw to its metering completion position. CONSTITUTION:A detection signal of the position of a main screw 16, which kneads, heats and melts resin stock during metering process, is sent from a position sensor 26 to a comparator 32. At every successive changing-over of the rotational frequency of a screw feeder 14 as the positional interval of the main screw 16 approaches its metering completion position, the comparator 32 compares a set signal of the position, which is inputted from a rotational frequency changing-over position setter 22, with the detection signal of the position of the main screw, which is inputted from the sensor 26, so as to output the rotational frequency changing-over signal when both the signals coincide with each other. A control unit 34 outputs a control signal, which corresponds to the rotational frequency set by a rotational frequency setter 20, to a motor 12 so as to successively decreasingly change the rotational frequency of the feeder 14 in order to feed resin stock filled in a hopper 10 as the supply, which is proper in response to the progress of the metering process, into an injection device.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to raw material supply control for a vented injection molding machine.
More specifically, the present invention relates to a raw material supply control method and apparatus for sequentially decreasing the rotation speed of a rotary raw material supply mechanism using a screw feeder during the metering process of a vented injection molding machine in correlation to the position of the main screw.

[Conventional technology]

A vent opening is provided in the center of the heating cylinder or barrel of the injection molding machine, and gases such as moisture and volatile substances contained in the resin raw material that is plasticized during the metering process are removed through the vent opening, resulting in injection molding. A vent-type injection molding machine that performs this is known.

The molding method using this type of vent-type injection molding machine is as follows: (1) Moisture, gas, and volatile substances such as monomers remaining in the molten material are removed, so molding defects such as silver streaks and air bubbles are avoided. It is possible to improve the appearance of products using transparent materials such as methacrylic resin (acrylic resin), and to perform good molding of flame-retardant grade products that particularly require the removal of gas content in TTN. (2) In addition, since pre-drying of the molding material can be omitted, operating costs and equipment costs for equipment required for pre-drying of resin are no longer required, and production efficiency can be improved. It has excellent injection molding technology.

However, due to the structure of the injection molding machine, molten resin tends to leak out from the vent opening where resin moisture and volatile substances are removed, which is called "venting up." When the removal operation is performed under reduced pressure,
The tendency for molten resin to leak during the metering process is increased. Therefore, when performing injection molding using a vent-type injection molding machine, it is important to avoid such vent-up and perform a stable metering process.

It is generally known that vent-up varies depending on the resin used and the main screw rotation speed of the injection molding machine.

In addition, even if the screw stroke required for metering changes depending on the size of the molded product, the leakage situation of the molten resin will differ, so the main screw rotation speed of the injection molding machine and the raw material supply amount, which are the conditions for venting up, will differ. The balance is often not constant.

Furthermore, when recycled materials are used by mixing them with new materials, the balance may differ each time. For this reason, in the past, the number of rotations of the screw feeder of the raw material supply device was adjusted empirically to control the raw material supply amount in order to avoid vent-up. Skill is required, and a lot of time is spent especially in the preparation stage before starting the molding process.Furthermore, the quality of the molded product may vary due to the inability to precisely set the rotation speed of the screw feeder of the raw material supply device. there were.

[Problem to be solved by the invention]

Unlike an extruder, the plasticizing process of an injection molding machine is performed after the main screw is retracted, so the effective feed section that preheats the raw material becomes shorter as metering progresses. Therefore,
As metering progresses, the retraction speed of the main screw decreases, albeit slightly, compared to the time at the start of metering (plasticization). This is a characteristic diagram showing changes in plasticizing ability as shown in the figure. Such a relationship also applies to vent-type injection molding machines. In other words, in order to avoid vent-up, it is necessary to set the rotation speed of the screw feeder that defines the raw material supply amount with sufficient consideration to plasticization near the screw stop position, and plasticization near the main screw rotation start position must be set. If the conditions are adjusted, the balance between the raw material supply amount and plasticization will be disrupted during the measurement, resulting in a vent-up condition.

Although it is possible to control the supply of raw materials according to the type and amount of resin based on experience with skill, taking into account such regulatory factors, ideally it is possible to control the supply of raw materials according to objective standards. It is desirable to do so. Since the metering process progresses by the backward movement of the main screw, the position of the main screw most appropriately reflects the progress of the metering process. Therefore, if the rotation speed of the rotary raw material supply mechanism in the metering process of a vented injection molding machine is correlated with the position of the main screw and the raw material supply is controlled, an extremely excellent raw material supply means can be realized.

Therefore, an object of the present invention is to provide a vent-type injection molding machine that avoids the vent-up that occurs during the metering process of a vent-type injection molding machine, and that allows stable injection molding to be performed regardless of the type or amount of resin used. The present invention provides a raw material supply control method and a raw material supply control device for a machine.

[Means to solve the problem]

The raw material supply control method for a vented injection molding machine according to the present invention includes a main screw for plasticizing and metering the raw material inserted into the barrel, a raw material supply device consisting of a screw feeder at the base of the main screw of the barrel, and further A vent opening is provided in a part of the barrel, and during the metering process, the screw feeder is rotated to supply raw material to the main screw and plasticize it, and the resulting molten raw material is desorbed at the vent opening. In a vent-type injection molding machine that is configured to inject into the mold after drying, the backward stroke position of the main screw during the metering process is detected, and as the stroke position of the main screw approaches the metering completion position, the main screw moves to the preset stroke position. It is characterized by sequentially decreasing the rotation speed of the screw feeder.

In the raw material supply control method for the vented injection molding machine described above, the backward stroke position of the main screw is divided into a plurality of arbitrary sections, the rotation speed of the screw feeder is set for each divided section, and the rotation speed of the screw feeder is set. can be reduced in stages.

In addition, the backward stroke position of the main screw is divided into multiple arbitrary sections, and the decreasing gradient of the rotation speed of the screw feeder is set for each divided section, so that the rotation speed of the screw feeder is continuously adjusted to the required slope. It can also be decreased.

Furthermore, it is also possible to set an arbitrary stroke position in the backward stroke of the main screw, and to continuously decrease the rotational speed of the screw feeder from this stroke position to the metering completion position. In this case, the rotational speed of the screw feeder can be decreased linearly or hyperbolically from the required stroke position to the metering completion position.

On the other hand, the raw material supply control device for implementing the method is
a position detector that detects the backward stroke position of the main screw; a rotation speed switching position setter that sets the backward stroke position of the main screw for switching the rotation speed of the screw feeder; a comparator that compares the stroke position detection value of the screw feeder with the stroke position setting value set by the rotation speed switching position setter and outputs a predetermined screw feeder rotation speed switching command signal when the two match; A rotation speed setting device that sets the rotation speed to be sequentially decreased and a screw feeder rotation speed setting value set by the rotation speed setting device based on a screw feeder rotation speed switching command signal output from the comparator. The present invention is characterized in that it includes a control section that controls the rotation speed of the drive motor of the feeder.

In the raw material supply control device for the vented injection molding machine described above, the rotation speed switching position setter sets a rotation speed switching position that divides the backward stroke position of the main screw into a plurality of arbitrary sections, and the rotation speed setting device The rotation speed of the screw feeder can be set to be decreased in stages at stroke positions in multiple sections.

In addition, the rotation speed switching position setter sets a rotation speed switching position that divides the backward stroke position of the main screw into arbitrary plural sections, and the rotation speed setting device sets the rotation speed of the screw feeder at the stroke position of each of the plural sections. It can be set to continuously decrease at a desired slope.

Furthermore, the rotation speed changeover position setter sets a rotation speed changeover position that divides the backward stroke position of the main screw into arbitrary multiple sections, and the rotation speed setting device sets the rotation speed changeover position to divide the backward stroke position of the main screw into arbitrary plural sections. The rotation speed of the screw feeder can be set to a constant value, and the rotation speed of the screw feeder can be set to decrease continuously from the predetermined stroke position to the metering completion position.

[Effect]

According to the raw material supply control method for a vented injection molding machine according to the present invention, during the metering process of the vented injection molding machine, the rotation speed of the screw feeder of the raw material supply device is sequentially decreased and changed depending on the position of the main screw. The amount of raw material supplied also decreases accordingly. This change type B can be objectively estimated and set according to the type and location of the resin, and an appropriate supply amount can be set according to the progress of the metering process. Furthermore, if appropriate programs are prepared for each type and amount of resin to be used, there is no need for preliminary studies, and the work can be carried out objectively and quickly without the need for skill.

〔Example〕

Next, regarding an example of the raw material supply control method according to the present invention,
Although a typical vent-type injection molding machine will be described below as an example, the present invention is not limited to this configuration.

FIG. 1 is an explanatory diagram showing a cross-sectional structure of a vent-type injection molding machine and a control system of a raw material supply control device, respectively, for carrying out the method of the present invention.

First, as an embodiment of the method of the present invention, the entire position section of the main screw during one process is set to 4, for example, as shown in FIG.
The rotational speed setting value of the screw feeder 14 is divided into two sections, N, , N2 . N, , N4, and the rotation speed switching position of the screw feeder 14 is set to S1 + 32 + Ss + 34 and SS, respectively, depending on the position of the main screw 16 (Sl is the measurement start position and S is the measurement completion position). .

Therefore, in FIG. 1, the resin raw material filled in the hopper 10 is supplied into the injection device by the rotation of the screw feeder 14 driven by the rotation of the motor 12, and the amount of this supply is determined by the rotation speed of the motor 12. be done. As the metering process progresses, the main screw 16 retreats from the metering start position to the metering completion position, and at the time of metering completion, the tip of the cylinder is filled with molten resin equivalent to one filling amount.

During the metering process, the resin raw material is kneaded by the rotation of the main screw 16 and is heated and melted. The resin is substantially in a molten state within the barrel 28 extending from the vicinity of the vent opening 18 to the tip of the main screw 16,
The metering process of injection molding proceeds while removing gas through the opening 18.

However, the rotation speed setting value and rotation speed switching position of the screw feeder 14 are set by a rotation speed setting device 20 and a rotation speed switching position setting device 22, respectively. The position of the main screw during the metering process is determined by a position detector 26 attached to the mounting plate 24.
Detected by. Note that as the position detector 26, a rotary potentiometer or the like combined with a movable rack can also be used.

The position detector 26 detects the position of the main screw 16 and sends this position detection signal to the comparator 32. Main screw 1
Each time the position section 6 is sequentially switched by the movement of the main screw 16, the comparator 32 compares the position setting signal and the position detection signal input from the rotation speed switching position setter 22 and the position detector 26, If they match, a rotation speed switching signal is output to the control section 34. The control unit 34 outputs a control signal corresponding to the rotation speed set by the rotation speed setting device 20 to the motor 12 every time the rotation speed switching signal is input, and controls the rotation speed of the motor 12 based on the content of this control signal. The rotation speed of the screw feeder 14 can be changed as shown in FIG. In this embodiment, a case is shown in which the rotational speed is controlled to be switched in four stages, but it goes without saying that the number of switching stages can be set to any number.

FIG. 3 shows another embodiment of the method of the invention.

That is, in this embodiment, the entire position section of the main screw 16 during the metering process is divided into four sections, and the rotation speed switching position of each screw feeder 14 is determined by the position of the main screw 16 as Sl * S2 + Sl.
+S4. Set S5. However, S is the measurement start position, S
, is the measurement completion position), the rotation speed of the screw feeder 14 is the rotation speed at each switching position NP+, NP2,
NPs, NP4° is set to proportionally decrease at a predetermined decreasing slope through NPs (zero). In this case, the rotational speed of the screw feeder 14 and the decreasing gradient switching position of the rotational speed are set by a rotational speed setting device 20 and a rotational speed switching position setting device 22, respectively (see FIG. 1). Therefore,
In this embodiment, the rotation speed setter 20 calculates a rotation speed reduction slope for each position section, which is the rate at which the rotation speed at the start position of the section decreases proportionally to the rotation speed at the end position of the section. Then, the rotation speed of the motor 12 within each position section is proportionally calculated in accordance with the decreasing slope in accordance with the position within the section, and is converted into a control signal instructing the rotation speed. In this way, in this example as well, as in the previous example,
By controlling the rotation speed of the motor 12, the rotation speed of the screw feeder 14 can be changed as shown in FIG.

In this embodiment as well, the number of rotation speed switching stages can be set to any number. In addition, the case where the rotation speed of the screw feeder 14 at each switching position is set and the slope is calculated to calculate and control the rotation speed for the position of the main screw 16 of the injection molding machine has been shown, but it is also necessary to set the slope itself. You can also do that. Furthermore, although the case where the rotation speed of the screw feeder 14 becomes zero at the metering completion position S is shown, it is also possible to set an arbitrary rotation speed at S.

FIG. 4 shows yet another embodiment of the method of the invention. That is, in this embodiment, the entire position section of the main screw 16 during the metering process is divided into two sections consisting of a constant speed section and a deceleration section. S respectively by
t, S2, and Sl (where Sl is the measurement start position and S is the measurement completion position), the rotation speed of the screw feeder 14 in the constant speed section is P+, and the rotation speed of the screw feeder 14 in the deceleration section is Pl. It is set to decrease proportionally from to zero at a predetermined decreasing slope. In this case, the rotation speed and metering start position Sl of the screw feeder 14 in the constant speed section, the deceleration start position S2 and the metering completion position S3 of the screw feeder 14 are determined by the rotation speed setting device 20 and the rotary switching position setting device 22, respectively. Therefore, in this embodiment, the rotation speed setting device 20 sets the rotation speed at a rate at which the constant speed rotation speed decreases proportionally to zero rotation speed at the measurement completion position. The slope is calculated, and the rotation speed of the motor 12 in the deceleration section is proportionally calculated in accordance with the position within the section according to the decreasing slope, and is converted into a control signal instructing the rotation speed. Note that in this embodiment, the rotation speed of the screw feeder 14 is higher than that of the main screw 1.
Although the case where the rotation speed is linear with respect to the position 6 is shown, it is also possible to set the rotation speed to be decelerated hyperbolically. However, when decelerating the rotation speed in a hyperbolic manner, the rotation speed of the screw feeder 14 in the deceleration section is calculated by correlation according to a predetermined hyperbolic function in accordance with the position within the section, and control is performed to instruct the rotation speed. Convert it to a signal.

〔Effect of the invention〕

As is clear from the various embodiments described above, according to the present invention, the metering stroke changes depending on factors such as the type of resin used, the rotation speed of the main screw of the vented injection molding machine, and the size of the molded product. Even if the vent-up condition is different, the rotation speed of the screw feeder of the raw material supply device can be arbitrarily set in a multi-stage program in correlation with the main screw position of the injection molding machine's metering stroke. It is possible to precisely control the amount of increase that you want to generate. Moreover, since the rotation speed of the screw feeder of the raw material supply device is controlled by the position of the main screw of the injection molding machine, the stability of the molded product quality can be ensured through repeated plasticization, which allows mass production of molded products. and contribute to cost reduction.

Furthermore, depending on the resin used and the state of the resin, the relationship between plasticizing ability varies depending on the amount of heat absorbed by the material at the feed section of the main screw, so the characteristic diagram of plasticizing ability (Figure 5) shows various forms. However, the rotation speed of the screw feeder cannot be easily adjusted due to changes in factors such as the N class of the resin used, changes in the screw rotation speed of the vented injection molding machine, and the size of the molded product. can.

Therefore, in combination with a decrease in the main screw's retraction speed, that is, a decrease in the main screw's resin discharge amount, the feeder is supplied with a commensurate amount of raw material by decelerating the screw feeder, and the ratio of raw materials sent to the main screw is always constant. Therefore, the state of supply of raw material from the main screw to the vent opening is always constant, and the occurrence of a vent-up condition can be effectively prevented.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the cross section of the vent type injection molding machine constructed according to the present invention and the raw material supply control system;
The figure is an operating characteristic diagram showing one embodiment of the raw material supply control system of the present invention, FIG. 3 is an operating characteristic diagram showing another embodiment of the raw material supply control system of the present invention, and FIG. FIG. 5 is an operating characteristic diagram showing yet another embodiment of the raw material supply control system. FIG. 5 is a characteristic diagram showing the relationship between the main screw position and the plasticizing capacity. In Fig. 2, N1 to N indicate arbitrarily set screw feeder rotational speeds, 82 to S4 indicate rotational speed switching positions, and in Fig. 3, 82 to S4 indicate rotational speed decreasing gradient switching positions, N
P, ~NP indicate the screw feeder rotational speed of an arbitrarily set gradient, and in FIG. 4, N2 indicates the screw feeder deceleration start position. 10... Hopper 12... Motor 14... Screw feeder 16... Main screw 18... Vent opening 20... Rotation speed setting device 22... Rotation speed switching position setting device 24...・Mounting plate 26...Position detector 28...Barrel 32...Comparator 34...Control unit FIo, 3

Claims (10)

[Claims] (1) A main screw for plasticizing and measuring the raw material is inserted into the barrel, a raw material supply device consisting of a screw feeder is installed at the base of the main screw of the barrel, and a vent opening is provided in a part of the barrel, and the metering process A vent-type injection system configured to rotationally drive a screw feeder to feed the raw material to the main screw and plasticize the raw material, and the resulting molten raw material is degassed at the vent opening and then injected into the mold. In the molding machine, the backward stroke position of the main screw in the metering process is detected, and as the stroke position of the main screw approaches the metering completion position, the rotation speed of the screw feeder is sequentially decreased at a preset stroke position. A raw material supply control method for a vent-type injection molding machine. (2) The method according to claim 1, wherein the backward stroke position of the main screw is divided into a plurality of arbitrary sections, the rotation speed of the screw feeder is set for each divided section, and the rotation speed of the screw feeder is gradually decreased. A method for controlling the supply of raw materials to a vent-type injection molding machine. (3) Divide the backward stroke position of the main screw into multiple arbitrary sections, set the decreasing gradient of the rotation speed of the screw feeder for each divided section, and continuously increase the rotation speed of the screw feeder to the required slope. A raw material supply control method for a vented injection molding machine according to the claim. (4) The vented injection molding machine according to claim 1, wherein an arbitrary stroke position is set in the backward stroke of the main screw, and the number of revolutions of the screw feeder is continuously decreased from this stroke position to the metering completion position. Raw material supply control method. (5) The raw material supply control method for a vented injection molding machine according to claim 4, wherein the number of revolutions of the screw feeder is linearly decreased from a required stroke position to a metering completion position. (6) The raw material supply control method for a vented injection molding machine according to claim 4, wherein the rotational speed of the screw feeder is hyperbolically reduced from a required stroke position to a metering completion position. (7) A main screw for plasticizing and measuring the raw material is inserted into the barrel, a raw material supply device consisting of a screw feeder is provided at the base of the main screw of the barrel, and a vent opening is provided in a part of the barrel, and the measuring process A vent-type injection system configured to rotationally drive a screw feeder to feed the raw material to the main screw and plasticize the raw material, and the resulting molten raw material is degassed at the vent opening and then injected into the mold. In a molding machine, a position detector detects the backward stroke position of the main screw, a rotation speed switching position setting device sets the backward stroke position of the main screw for switching the rotation speed of the screw feeder, and detection is performed by the position detector. a comparator that compares the detected stroke position value of the main screw and the stroke position setting value set by the rotation speed switching position setter and outputs a predetermined screw feeder rotation speed switching command signal when the two match; , a rotation speed setting device for setting the rotation speed of the screw feeder to be sequentially decreased; and a rotation speed of the screw feeder set by the rotation speed setting device based on a screw feeder rotation speed switching command signal output from the comparator. 1. A raw material supply control device for a vent-type injection molding machine, comprising a control section that controls the rotation speed of a drive motor of a screw feeder based on a set value. (8) The rotation speed switching position setter sets a rotation speed switching position that divides the backward stroke position of the main screw into arbitrary multiple sections, and the rotation speed setting device sets the rotation speed of the screw feeder at the stroke position of each of the multiple sections. 8. The raw material supply control device for a vent type injection molding machine according to claim 7, wherein the control device is configured to reduce the amount in stages. (9) The rotation speed switching position setter sets the rotation speed switching position that divides the backward stroke position of the main screw into arbitrary multiple sections, and the rotation speed setting device sets the rotation speed of the screw feeder at the stroke position of each of the multiple sections. 8. The raw material supply control device for a vented injection molding machine according to claim 7, wherein the control device is configured to continuously decrease each of the amounts at respective required gradients. (10) The rotation speed switching position setter sets the rotation speed switching position that divides the backward stroke position of the main screw into arbitrary plural sections, and the rotation speed setting device sets the rotation speed switching position to divide the backward stroke position of the main screw into arbitrary plural sections. The raw material supply control for a vented injection molding machine according to claim 7, wherein the rotation speed of the screw feeder is set to a constant value, and the rotation speed of the screw feeder is set to decrease continuously from the predetermined stroke position to the metering completion position. Device.