JPS5926462B2 - Thermoplastic resin molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermoplastic resin molding apparatus that injects thermoplastic resin into a cavity through a plurality of gates to mold the resin.

In traditional injection molding systems, the cylinder temperature,
Temperature conditions such as nozzle temperature and mold temperature are generally controlled by a temperature controller, and pressures such as injection-next pressure, injection secondary pressure, back pressure, etc. are generally controlled by hydraulic pressure regulating valves, and injection-next time, injection secondary time, etc. This method uses a timer or stroke adjustment to set each, and performs sequence control to repeat the molding cycle.

In this control system, melting occurs due to changes in resin temperature, mold temperature, hydraulic oil viscosity changes, injection speed changes due to hydraulic oil viscosity changes, and changes in resin polymerization degree due to changes in ambient temperature. Since there is no ability to automatically change the setting conditions in response to changes in resin viscosity, etc., defective products are often produced continuously.

Therefore, operators are required to find defective products as quickly as possible and correct the conditions so that non-defective products can be obtained.

However, unless a defective product appears, changes in molding conditions due to external disturbances cannot be detected, and although it is possible to quickly detect external defects, dimensional and mechanical defects cannot be detected. I am always late.

Furthermore, in these days when there is an urgent need for automation and unmanned injection molding due to working conditions and labor shortages, it is extremely difficult to unmanned molding because there is no appropriate means to deal with the occurrence of defective products. There is.

Therefore, recently, several measures have been proposed to correct the setting conditions in response to changes in conditions due to disturbances.

For example, by automatic adjustment of screw speed and back pressure,
A method of equalizing the molten resin viscosity and injection amount, or a method of shifting from injection-secondary pressure to secondary injection pressure when the resin pressure injected into the cavity reaches an arbitrary set pressure, or a method of making the injection pressure uniform. A method of detecting the resin pressure, injection unevenness hydraulic pressure, and injection time, converting it into an electrical signal, and using a computer to find the conditions that optimize the three factors and feeding it back to the machine. A method of providing a constant filling state of resin in the cavity by applying an injection pressure commensurate with the resistance and an injection speed commensurate with the injection pressure.Furthermore, the injection process is controlled by program control, and at the same time, the cavity is The system measures the resin pressure inside the tee and automatically changes the program if a malfunction occurs.

There are many other similar methods, but the basics of these control methods can be summarized in one of the following points.

1. Uniformity of molten resin viscosity.

2. Changing the injection pattern in response to changes in molten resin viscosity.

3. Control of injection pattern by resin pressure inside the cavity.

All of these methods are extremely effective for single-cavity molds or multi-cavity molds with the same resin flow state and pressure distribution in each cavity, but in reality, In a multi-cavity mold, it is extremely rare that the resin flow state and pressure distribution in each cavity are the same.

In particular, in hot runner molds, the temperature distribution of the hot runner block constantly changes, so it is difficult to accurately distribute the resin energy supplied from the nozzle of the molding machine to each gate in the mold. It is impossible to divide the number equally into , and it becomes meaningless to use the various methods described above.

In other words, in either method, for example, when adjusting the energy applied to the resin (injection pressure, cylinder temperature, screw rotation speed, etc.), there is no need to make any adjustments to the individual energy distributed to each gate in the mold. Since there is no method, the effect of automatic control of molding conditions is extremely small.

In another example, a pressure transducer is installed in the mold to detect the resin pressure in the cavity, and when the resin pressure in the cavity reaches a certain arbitrary pressure, the pressure is transferred from the injection process to the pressure holding process. This is an excellent method among the many injection process pattern control methods, but for example, when molding is performed using a two-cavity mold, the resin filling state of the two cavities is different, resulting in a time-consuming process. If the relationship between elapsed time and pressure is as shown in Figure 1, the time to reach the set pressure p is tl in one cavity and t2 in the other, and at which point the holding pressure changes from the injection process. Even if the process moves on, the product obtained from either cavity is problematic.

Therefore, the various methods described above are effective in molding using a single-piece mold with a single-point gate, but when molding with multiple pieces,
Alternatively, there is little effect when using a mold with multiple gates.

On the other hand, recent advances in runnerless molding systems have been remarkable, and there is a method that makes it possible to eliminate gate clogging and resin dripping, which are the disadvantages peculiar to hot runners, by using a hot runner/cold gate method. .

That is, a heating element with excellent heat generation characteristics and a sharp tip is provided in the gate part, and immediately before the start of the injection process A, an appropriate voltage is applied to this heating element according to the resin used to generate heat. Make the resin in the gate part flowable and start injection.

After heating the heating element, the power supply to the heating element is stopped when an arbitrary set time has elapsed, and the resin stagnant in the gate immediately exchanges heat with the mold and is cooled and solidified.

Therefore, since the gate part is solidified when the mold is opened, there is no need to worry about nasal drip.Also, since the gate part is forcibly heated, the resin at the gate part remains solidified and the resin does not flow into the cavity. There is no so-called gate jam that prevents entry.

However, in a multi-cavity mold, there are gates where the resin flows smoothly and gates where the resin flows poorly due to changes in temperature conditions, and even if there is a difference in the filling state of resin in each cavity, the same Sometimes, we do not have a suitable way to control this flow condition in order to start heating the heating element and stop heating the heating element at the same time.

In other words, differences in the fluidity of the resin at the gate part, which are fixed to some extent such as the gate diameter and the heating characteristics of the heating element, can be made uniform by adjusting the voltage and current applied to the heating element in advance. It is impossible to correct even if there is a difference in the flow state of the resin between each gate or each cavity due to a change in the temperature distribution of the hot runner block or a change in the mold temperature distribution. Furthermore, this method does not provide any countermeasures against changes in the viscosity and pressure of the resin injected from the nozzle of the molding machine.

As is clear from the above description, a molding system that can control the filling state of resin between each cavity in multi-individual resin molding has not yet appeared.

On the other hand, in the case of small articles, most of the molds actually used are made of multiple molds and generally have strict dimensional accuracy.

In addition, even for large items that require strict dimensional accuracy, we are increasing the number of sets.

Therefore, it is an important issue not only to stabilize the dimensions of the product between each shot, but also to equalize the filling state between the cavities in the same shot, that is, to equalize the dimensions of the molded product.

Therefore, an object of the present invention is to continuously produce weight-wise and dimensionally stable molded products in multi-cavity thermoplastic resin molding.

The present invention will be explained based on examples.

FIG. 2 is a partial sectional view of an example of an injection mold for implementing the present invention.

a heating element 2 attached to a hot runner block 1;
2 and its tips 3, 3' electrically generate heat, and the tips 3, 3' in particular have good heat generation characteristics.

The heating element tip portions 3, 3' are positioned approximately at the center of the gate portions 4', 4' provided on the stationary mold plate 4.

Pin 6゜6 that forms part of the cavity surface of the movable template 5
' is fitted into the movable mold plate 5, one end of which is in contact with the pressure detection ends 9, 9' of the pressure transducers 8, 8' provided on the backup plate 7, and the pin 6°6' is in a state where it can slide on the movable template 4.

When molding is performed using such a mold, the hot runner block 1 and the central portions of the heating elements 2, 2 are heated in advance, and the tips of the heating elements 2, 2' are heated at an arbitrary time immediately before injection starts. , 3' and injection is performed, the resin passes through the nozzle 10, sprue bush 11, hot runner block 1, and is fed into the cavities 12, 12' from the gate.

At this time, it is naturally possible that the resin filling state of the two cavities 12 and 12' will differ depending on the temperature distribution of the hot runner block 1, the difference in the diameter of the two gates, the temperature difference in the gate portion, and the like.

In that case, the relationship between resin pressure inside the cavity and time is the third
obtained as shown and confirmed by a pressure transducer.

t3 is the time when the resin pressure in one cavity reaches a preset predetermined pressure, t4 is the time when the resin pressure in the other cavity reaches the preset pressure, and to is the time when the resin pressure in the other cavity reaches the preset pressure. This is the standard time for the resin pressure to reach the preset pressure.

The difference t between this standard time to and the times t3 and t4 at which the resin pressure in each cavity reaches the set pressure.

-t9 and to-t4 are converged to zero.

In other words, by using this time difference, the heat generation amount of the heating element in the gate part or the timing of heat generation can be adjusted to control the temperature of the resin in the gate part at the start of injection, and the flow state of the resin in the gate part can be made uniform. The gist of the present invention is to make the relationship between resin pressure and time the same in all cavities.

FIG. 4 shows an example of a circuit for controlling the heating timing of the heating elements 2, 2'.

RX is a relay contact that closes instantaneously at the start of mold closing, Ry is a relay contact that is closed from the start of injection to the completion of holding pressure, R
z is the contact point of the relay that is closed from the time the resin pressure in the cavity reaches the set pressure to the completion of pressure holding, and TLl sets the standard time from the start of injection until the resin pressure in the cavity reaches the set pressure. The timer TL2 is a timer that sets the time from the start of mold closing to the heating of the heating element in the gate section.Ml and M2 are motors connected via gears to a dial that changes the set time of TL2, and the motors Ml, Motor M2 rotates in opposite directions, and motor M1 rotates a dial in a direction that increases the set time of timer TL2.

R1 and R2 are relays.

When mold closing starts, the a contact of relay Rx is closed,
Relay R2 is energized and is self-maintained through its contacts.

At the same time, timer TL2 starts timing.

When timer TL2 completes timing, a of timer TL2
The contacts are closed, voltage is applied to the tip of the heating element via the transformer and variable resistor, and heat generation begins.

As time progresses further and injection starts, the a contact of the relay Ry is closed and the timer TL1 starts timing.

When the resin pressure in the mold reaches the set pressure before timer TL1 completes timing, Ry closes before the b contact of timer TLI opens, relay R1 is energized, and relay R1
The a contact of the relay R1 is closed, the a contact of the relay R1, and the timer T are closed.
The motor M1 is energized through the b contact of L1, and the timer T
Motor M1 rotates until L1 completes timing,
Increase the setting time of timer TL2.

Conversely, if the timer TL1 completes timing before the resin pressure in the mold reaches the set pressure, the motor M2 is energized through the B contact of the relay R1 and the A contact of the timer TLI.
Motor M2 rotates until the resin pressure in the mold reaches the set pressure and the b contact of relay R1 opens, and timer TL2
Shorten the setting time.

When the resin pressure inside the mold reaches the set pressure, relay R1 is activated.
The b contact of the timer TL2 is opened, and at the same time the a contact of the timer TL2 is opened, and energization to the heating element is stopped.

Further, when the pressure holding is completed, the contacts of the relays Ry and Rz are opened, and the circuit returns to its original state.

In this way, if the resin pressure in the mold reaches the set pressure earlier than the set time of timer TL1, the set time of timer TL2 will gradually increase, the timing of heat generation of the heating element in the gate part will be delayed, and the gate part at the time of injection will be delayed. The fluidity of the resin deteriorates, and the time it takes for the resin pressure in the mold to reach the set pressure is gradually delayed.

In addition, if the resin pressure in the mold reaches the set pressure later than the time set by the timer TLI, the fluidity of the resin at the gate will improve, and the time for the resin pressure in the mold to reach the set pressure will gradually increase. It gets faster.

In this way, the time set by the timer TL2 is dynamically adjusted so that the time set by the timer TL1 is equal to the time from the start of injection until the resin pressure in the mold reaches the set pressure. be adjusted.

It is possible to adjust the temperature of the resin in the gate part using a heating element installed in the gate part, and it is possible to adjust not only the timing of heat generation, but also the voltage applied to the heating element and the current flowing.
In addition, the method of feeding back the difference between the time required for the resin pressure in the cavity to reach the set pressure and the standard time to the heat generation amount and heat generation start timing of the heating element is not limited to the analog method as in the example, but also the pulse signal method. This is also easily possible using a digital method.

Further, the embodiment in which the heat generation timing of the heat generating element in the gate section is adjusted is related to one pressure detection device and one heat generation element, and the second embodiment using two heat generation elements and two pressure detection devices is related to one pressure detection device and one heat generation device.
In the case of molding using the mold shown in the figure, by providing two circuits as shown in Figure 4 and setting the same value for the two standard time setting timers, the resin pressure in the two cavities can be adjusted. can be adjusted simultaneously to reach the set pressure.

By obtaining such a state, the resin filling state of the two cavities can be easily controlled using a conventional injection molding condition control device.

Although the example describes molding using a two-cavity mold, it is easy to see from the above explanation that the resin filling state can be controlled in the same way for a mold using three or more cavities. You can probably understand it.

In addition, even if one molded product, that is, a cavity, has multiple gates, if the resin filled from each gate forms a relatively uniform part of the molded product, the present invention can be applied. can be applied.

FIG. 5 shows an example of its application, with reference numeral 13 indicating a product, 14 indicating a position where a gate is provided, and 15 indicating a location where a pin for transmitting pressure to a pressure transducer is provided.

As is clear from the above description, according to the thermoplastic resin molding apparatus of the present invention, the resin filling state in the cavity can be easily controlled even in molding using a mold having a plurality of gates.

Further, for this reason, it is possible to obtain a molded product with high accuracy in terms of weight and dimensions, and it is also possible to obtain effects such as automation and unmanned molding possible.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the resin pressure inside the cavity and time in the case of two moldings using the conventional molding method, Fig. 2 is a partial cross-sectional view of a mold device according to an embodiment of the present invention, and Fig. 3 is a diagram showing the relationship between the molding device and the time in the case of two-cavity molding using a conventional molding method. FIG. 4 is a control circuit diagram for controlling the mold apparatus, and FIG. 5 is a plan view of the molded product. 2, 2'... Heating element, 4... Fixed side mold, 4', 4
'...Gate part, 5...Movable side mold, 8,8'...
・Pressure transducer, 12, 12'...cavity.

Claims (1)

[Claims] 1. A mold device including a plurality of gate parts each having a heating element and a pressure detection device for detecting the pressure inside the cavity of resin injected from each of the plurality of gates, and A thermoplastic resin molding apparatus comprising: a control device that controls the function of the heating element based on a signal transmitted from the heating element;