JPH0467493B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a temperature control method for an injection molding machine, and particularly to temperature control when a single cavity has multiple hot runner gates, so-called multi-point gates. It is about the method.

[Prior art and its problems]

Hot runners are often used in injection molding machines to heat the runner and keep the resin passing through it in a molten state.When using this hot runner method with multi-point gates, it is necessary to precisely control the temperature of each gate. It is important to control this in order to stabilize the quality of molded products. For this reason, conventionally, the temperature of each gate was detected and the current flowing through each heating element was individually controlled so that the detected temperature reached a predetermined temperature.

However, in such an individual control method, the temperature of each gate is not necessarily maintained in a constant relationship due to control deviations, etc., so the amount of resin flowing out from each gate varies depending on the shot, and the position of the weld line changes. It has been difficult to highly stabilize the quality of molded products.

[Means for solving problems and their effects]

The present invention was made to solve the problems of the prior art as described above, and its control method is as follows:
The multiple nozzle chips constituting the multi-point gate are divided into main nozzle chips and slave nozzle chips, and
A relationship setting means is provided to determine the relationship between the current flowing through the heating element of the main nozzle chip and the current flowing through the heating element of the slave nozzle chip. The slave nozzle chip is characterized in that the relationship setting means controls the current flowing through the heating element of the main nozzle chip while maintaining a predetermined relationship with the current flowing through the heating element of the main nozzle chip.

In this way, the temperatures of each gate are collectively controlled while maintaining a predetermined relationship, so the relationship between each gate is always the same, and variations in quality from shot to shot can be extremely reduced.

〔Example〕

FIG. 1 shows an embodiment of the invention. In the figure, 11 is a mold of an injection molding machine, 12 is a cavity therein, 13A to 13C are gates, and 14A to 1
4C is a nozzle tip. In this example, 14B is a main nozzle chip, and 14A and 14C are sub nozzle chips. Each nozzle tip 14A to 14C
consists of a chip core 15 and a chip outer cylinder 16,
Each chip core 15 has built-in resistance heaters 17A to 17C, respectively. That is, each nozzle tip 14A to 14C is of an internal heating type, and a hot runner 18 is provided between the tip core 15 and the tip outer cylinder 16 to keep the resin in a molten state. Also, a temperature sensor (usually a thermocouple) 19 is built into the chip core 15 of the main nozzle chip 14B to detect the temperature at its tip (corresponding to the temperature of the gate). Each nozzle tip 14A-14C is connected to a manifold (not shown).

Further, 20 is an AC power supply for the heaters 17A to 17C, 21 is a triax for controlling applied voltage, and 22
A to 22C are variable resistors for setting the current ratio, 23 is a comparator between the output of the temperature sensor 19 and the set value, 24
is a phase control circuit that controls the firing phase of the triac 21.

Temperature control of each gate 13A to 13C is performed as follows. That is, the main nozzle tip 14B
Then, the temperature of the gate 13B is detected by the temperature sensor 19, the detected value and the set value are compared by the comparator 23, and the difference is inputted to the phase control circuit 24.
The phase control circuit 24 controls the firing phase of the triac 21 according to the difference, and controls the applied voltage, that is, the current flowing to the heater 17B. In other words, in the main nozzle chip 14B, feedback control is performed to reduce the current flowing through the heater 17B when the temperature of the gate 13B is higher than the set value, and to increase the current flowing when the temperature is lower than the set value.

On the other hand, in the slave nozzle chips 14A, 14C, a voltage controlled by the triax 21 is applied to the heaters 17A, 17C, and the variable resistors 22A,
22B allows a regulated current to flow. In other words, a current that is maintained at a predetermined ratio with respect to the current flowing through the heater 17B flows through the heaters 17A and 17C by the variable resistors 22A to 22C.
The temperature of the gate 13B is controlled to be maintained in a predetermined relationship with the temperature of the gate 13B.

In multi-point gates, it is necessary to determine the temperature of each gate according to the cavity shape, gate position, gate characteristics, etc., but if the above control is performed, the temperature of each gate can be set in advance. Since batch control can be performed while maintaining a predetermined relationship, the quality of each shot can be stabilized.

FIGS. 2 and 3 each show other embodiments of the invention. In these figures, parts corresponding to those in FIG. 1 are given the same reference numerals. Although the mold, cavity, gate, nozzle chip, etc. are not shown and only the electrical system is shown, the heaters 17A to 17C correspond to the respective nozzle chips and gates, as in FIG. 1.

In the embodiment of FIG. 2, each heater 17A to 17C
The applied voltages of the triaxes 21A to 21 are respectively
C, the triaxes 21A to 21
The ignition phase of each of C is individually controlled by phase control circuits 24A to 24C. The current flowing through the heater 17B of the main nozzle chip is feedback-controlled by the comparator 23, the phase control circuit 24B, and the triax 21B in accordance with the output of the temperature sensor 19, as in the case of FIG. 17A, 17C
The energizing currents are controlled by phase control circuits 24A and 24C, respectively, which generate output phases having a predetermined relationship with the output phase of phase control circuit 24B. The relationship between the output phase of phase control circuit 24A and the output phase of phase control circuit 24B, and
The relationship between the output phase of 24C and the output phase of 4B is set in advance in consideration of the shape of the cavity, the position of the gate, etc.

Compared to the control method shown in FIG. 1, this control method does not use a variable resistor, so power loss is small.

In the embodiment of FIG. 3, the slave nozzle chip also includes temperature sensors 19A, 19C and comparators 23A, 23C.
and the phase control circuits 24A, 24 depending on the temperature.
The output phase of C is corrected.
The rest of the configuration is the same as that in FIG. 2. This control method is effective when it is necessary to change the relationship between the currents flowing between the main nozzle chip heater 17B and the slave nozzle chip heaters 17A and 17C depending on the temperature.

In the above embodiment, the case where the number of gates, that is, the number of nozzle chips is three, has been described, but the present invention is not limited to this, and can be applied to any case where one cavity has two or more gates.

Further, in the above embodiment, a case has been described in which an internally heated nozzle tip is provided, but the present invention is equally applicable to an externally heated nozzle tip.

Further, in the above embodiment, a case has been described in which a resistance heater is used as the heating element of the nozzle tip, but the present invention can be similarly applied to a case where an induction heating coil is used as the heating element.

〔Effect of the invention〕

As explained above, according to the present invention, a plurality of nozzle chips constituting a multipoint gate are divided into a main nozzle chip and a sub nozzle chip, and the main nozzle chip detects the temperature of the gate and energizes the heating element according to the temperature. In the secondary nozzle chip, the current flowing through the heating element of the main nozzle chip is controlled so as to maintain a predetermined relationship with the current flowing through the heating element of the main nozzle chip, so that the temperature of each gate maintains a predetermined relationship. Therefore, the relationship between each gate is always maintained in almost the same state, which has the advantage of highly stabilizing the quality of the molded product for each shot.

[Brief explanation of the drawing]

1 to 3 are control system diagrams each showing an embodiment of the control method of the present invention. 11~Mold, 12~Cavity, 13A, 13
B, 13C~gate, 14B~main nozzle chip,
14A, 14C - slave nozzle chip, 17B - main nozzle chip heater, 17A, 17B - slave nozzle chip heater, 19 - temperature sensor, 20 - AC power supply, 21, 21A, 21B, 21C - triax, 22A, 22B, 22C - variable Resistor (related setting means), 24, 24B ~ phase control circuit, 2
4A, 24C - phase control circuit (relationship setting means).

Claims (1)

[Claims] 1. A plurality of nozzle chips constituting a multi-point gate are divided into a main nozzle chip and a sub-nozzle chip, and a relationship setting means is provided for determining the relationship between the current flowing through the heating element of the main nozzle chip and the current flowing through the heating element of the sub-nozzle chip; In the main nozzle chip, the temperature of the gate is detected and the current flowing through the heating element is controlled according to the detected temperature, and in the secondary nozzle chip, the heating element is heated while maintaining a predetermined relationship with the current flowing through the heating element of the main nozzle chip using the above-mentioned relationship setting means. A method for controlling the temperature of a multi-point gate in a hot runner, characterized in that the current flowing through the element is controlled.