JPH0427934B1 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to plastic injection molding equipment, and more particularly to hot runner injection molding equipment.

(Prior technology) The resin filled in the resin passage connecting the nozzle of the molding machine and the mold cavity, the so-called runner, is cooled and solidified together with the resin (product) filled in the cavity, and when the mold is opened, it is released together with the product outside the mold. In contrast to the so-called cold runner molding system where the runner is kept in a molten state, only the resin inside the cavity is cooled and solidified and then discharged outside the mold, and the molten runner is used for the next molding cycle. A hot runner type injection molding system is known in which the inside of a cavity is filled.

In such hot runner injection molding, "cutting" of the resin at the gate portion when the mold is opened poses a problem. Specifically, it is known that the resin passage from the nozzle of the molding machine to the gate of each cavity is heated from the outside with a resistance heater to keep the resin in a molten state. The close part is close to the cavity plate, which is generally constantly cooled by cooling water, so it is extremely difficult to keep the resin temperature near the gate hole constant due to the large temperature fluctuations caused by the opening and closing operations of the mold. However, there were problems such as the resin temperature being too high and the resin pulling strings, or the resin solidifying and clogging the gate hole, making subsequent injections impossible. Furthermore, if the resin temperature is too high, a so-called "avalanche" phenomenon occurs in which resin leaks from the gate hole during mold opening.

To solve this problem, a mechanical valve is installed at the gate, which applies enough heat to keep the resin near the gate in a molten state, and closes the valve when the mold is opened to prevent stringing of the resin. A device designed to prevent avalanches has been developed, but as is well known, high pressure is applied near the gate, and the valve has to be opened and closed a huge number of times, so it is prone to failure. be. Another drawback is that the device becomes bulky due to the use of a valve with a complicated structure.

In addition, a pointed heating element is placed in the resin passage near the gate hole so as to face the gate hole, and when the mold is opened, the resin in the gate hole is actively cooled and solidified, allowing the resin to flow through the gate hole when the mold is opened. The so-called intermittent heating method prevents the resin from leaking, prevents stringiness, and heats the heating element to a high temperature just before injection in the next cycle to remelt the solidified resin in the gate hole and enable injection. A hot runner injection molding machine is also known, but in this machine it takes time to remelt the solidified resin inside the gate.
Since the heating element is placed in the resin passage, there is a significant loss of injection pressure.Especially when molding with resin containing glass fibers, there are various problems such as the tip of the heating element being damaged or worn out. There is. Furthermore, when trying to apply sufficient heat to the tip of the heating element to instantaneously re-melt the solidified resin inside the gate, the base of the heating element inevitably becomes hotter than the tip, causing the resin around the base to burn. There is also the problem of decomposition.

In addition, all conventional hot runner injection molding machines heat a desired heating area, such as a gate hole, by heat transfer from a resistance heater, so the thermal response is poor and the desired heating area cannot be heated. It is extremely difficult to control the temperature to the same temperature as the gate hole of each cavity (maintaining the so-called gate balance), especially in the case of a multi-cavity mold with multiple cavities.
It was extremely difficult. Furthermore, resistance heating heaters have the disadvantage that wire breakage occurs frequently because they generate heat through self-resistance.

Previously, the present applicant was able to accurately control the resin temperature near each gate hole of a mold with multiple cavities, and maintain a good gate balance. String pulling without using complicated mechanisms such as intermittent heating of holes.
He invented and filed an application for a hot runner injection molding device that allows for good molding without causing avalanches, gate clogging, etc. (Special application 1986-37121
In the hot runner type injection molding equipment, the part of the resin passage (generally consisting of a sprue part and a runner part) that connects the nozzle of the molding machine and each cavity in the mold, adjacent to the gate hole of each cavity, It is formed by a pipe-shaped member made of a material that can be heated by high-frequency induction heating. A high-frequency induction heating coil is wound around each pipe-shaped member, and the heating coils are connected in series to a high-frequency power supply means. Further, a control means is provided for controlling the temperature of the pipe-shaped member by controlling the electric power supplied to the heating coil.

When a high frequency current is supplied to the heating coil from the power supply means, the pipe-shaped member generates heat due to electromagnetic induction. Heating the pipe-shaped member by the heat generated by electromagnetic induction has a better thermal response than heating by heat transfer from the resistance heater. In other words, in the case of heat conduction from the heater, when the temperature of the pipe-shaped member reaches a predetermined temperature, the heater has become even hotter, and the temperature of the pipe-shaped member will continue to rise even after the power supply to the heater is stopped. There is a delay time due to the ringing phenomenon in which the temperature of the pipe-shaped member continues to drop even if the heater is turned on when the temperature of the pipe-shaped member has decreased, but when induction heating is used, the pipe-shaped member itself heats up. Moreover, since the rate of heat generation is extremely fast, there is no risk of linking, and temperature control can be achieved extremely well. In addition, in the case of heat conduction from the heater, the temperature of the heated member changes greatly depending on the contact condition between the heater and the heated member (pipe-shaped member), whereas in the case of heating by electromagnetic induction, the temperature of the heated member changes greatly depending on the contact condition between the heater and the heated member (pipe-shaped member). The minute positional relationship between the heated parts has almost no effect on the temperature of the heated parts, so the resin temperature near each gate hole can be controlled with high precision, and gate balance can be maintained extremely easily. It has the feature of becoming. Furthermore, since the induction heating coil is simply a wound conductor, it can be wound to a position fairly close to the gate hole, and therefore heat can be directly generated to a portion of the pipe-shaped member fairly close to the gate hole. Therefore, the temperature difference between the tip (portion close to the gate hole) and the base (portion away from the gate hole) of the pipe-shaped member can be made extremely small. Therefore, when the tip is heated to a temperature sufficient to keep the resin in the gate hole in a molten state, the temperature at the base rises too much, causing the resin in contact with that part to burn or decompose. There is no. Furthermore, when the heating coils are connected in series, it is particularly easy to maintain gate balance because changes in the resistance of one heating coil circuit due to aging, for example, affect the current flowing through all the heating coils. In other words, when each heating coil is connected to a power source in parallel, if the resistance of one heating coil circuit increases for some reason, the electric power applied to that coil decreases, and only the temperature of the pipe-shaped member around which that coil is wound increases. However, if the heating coils are connected in series, the power applied to all heating coils will be small, and therefore the temperature of all pipe-like members will drop almost uniformly, and the gate balance will be maintained extremely well. Easy to do. Also, experiments have shown that the number of turns for each heating coil is from a few turns to more than 10 turns, and if the coils are connected in parallel to a power supply, there is a problem that it is difficult to apply power because the load is small. Furthermore, the heat generated by the high-frequency induction heating coil depends on the coil's distance from the power supply, that is, the resistance loss of the line including skin effect, so when connecting each coil to the power supply in parallel, the distance of each coil from the power supply must be determined accurately. If the number of turns is adjusted to match the distance between the coils or the distance from the power supply of each coil is not adjusted, the gate balance will be lost. is advantageous. Furthermore, as mentioned above, in this device, the resin near the gate hole can be heated by simply winding the conductor wire around the pipe-shaped member from a few turns to more than 10 turns, so the structure around the gate becomes extremely simple. It is possible to easily convert molds with multiple molds for small products or molds with several gates per cavity into hot runners. The temperature control means for controlling the temperature of the pipe-shaped member to a desired value detects the temperature of the pipe-shaped member and adjusts the electric power supplied from the power supply means to the heating coil depending on the level of the temperature relative to a set value. An on-off circuit can be used.

As is well known, if the resin temperature near the gate hole can be precisely controlled, it is possible to find the critical resin temperature that will not cause resin leakage or stringiness from the gate hole when the mold is opened, and will not cause gate clogging. is easy for those skilled in the art, and therefore, with this device, good hot runner molding can be performed without using complicated mechanisms such as mechanically opening/closing valves or intermittent heating. In addition, unlike the intermittent heating molding equipment mentioned above, there is no need to place a heating element inside the resin passage, so there is less loss of injection pressure.
Furthermore, there is no failure of the device due to damage to the heating element, etc. In addition, since the heating coil used in the device has almost no self-resistance heat generation, there is no risk of disconnection, and there is almost no failure due to disconnection of the heater, which frequently occurs in conventional hot runner type molding devices.

As mentioned above, the hot runner type injection molding apparatus described in the above-mentioned Japanese Patent Application No. 59-37121 has many advantages, but depending on the shape of the individual mold, the design of the cooling water passage, etc. The gate balance may be slightly disturbed due to differences in heat transfer near the gate hole. In particular, when molding with a resin such as nylon where a slight difference in resin temperature has a large effect on the viscosity of the resin, even better gate balance may be desired.

(Object of the Invention) In view of the above circumstances, the present invention has been made to reduce the difference in temperature between each gate hole when there is a difference in temperature in the hot runner type injection molding apparatus as described above. The object of the present invention is to provide a hot runner type injection molding apparatus.

(Structure of the Invention) The apparatus of the present invention is characterized in that, in the hot runner injection molding apparatus as described above, a gate balance adjustment circuit can be connected in parallel to each heating coil.

A capacitor, coil, or resistor can be used as the gate balance adjustment circuit. For example, if a capacitor is connected in parallel to some of a plurality of heating coils, the temperature of the pipe-shaped member around which the heating coil is wound increases, and the temperature of the pipe-shaped member around which other heating coils are wound decreases. Further, when a coil or a resistor is connected in parallel to each of the heating coils, the temperature of the pipe-shaped member around which the heating coil is wound decreases, and the temperature of the pipe-shaped member around which the other heating coils are wound increases. Further, the magnitude of the temperature rise and fall at that time changes depending on the magnitude of the value of the gate balance adjustment circuit.

Therefore, by selectively connecting gate balance adjustment circuits in parallel to some of the plurality of heating coils and selecting the values of the elements, the gate balance among all the gates can be extremely finely adjusted. I can do it.

Note that if a resistor is used as a gate balance adjustment circuit, power loss will occur, and from that point of view a capacitor or a coil is preferable.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, a hot runner type injection molding apparatus according to an embodiment of the present invention has four cavities 12a,
A mold 10 having molds 12b, 12c, and 12d is provided. The mold 10 consists of a fixed half 14 fixed to a fixed die plate of a molding machine (not shown) and a movable half 16 fixed to a movable die plate, where the movable half 16 is connected to the fixed half 1.
4, that is, when the mold 10 is closed, the four cavities 12a to 12d are formed between the two halves 14 and 16. The stationary side half 14 includes a mounting plate 18 that is attached to the stationary die plate, a manifold block 22 that is press-fixed to the mounting plate 18 with the heat insulating material 20 in between, and a manifold block 22 that is press-fixed to the manifold block 22 with the support block 24 in between. It consists of a cavity plate 26.

The cavity plate 26 has four recesses 28a, 28b, 28c, which open toward the movable half 16.
It is equipped with 28d. These four recesses 28a-2
8d cooperates with the four cores 17a, 17b, 17c, and 17d provided in the moving half 16 to form the four cavities 12a to 12d. On the manifold block side of the cavity plate 26, there are four recesses 30a, 30b, 30c, 3 that open toward the manifold block so as to face the four recesses 28a to 28d, respectively.
0d is provided. In addition, the fixed half 14 has a molding machine nozzle (not shown) and each cavity 1.
2a to 12d are gate holes 32a, 32b, 32 formed at the bottom of each recess 30a to 30d, respectively.
A resin passage is formed which connects via c and 32d. This resin passage consists of a so-called sprue section 34a that is directly connected to the nozzle of the molding machine, and a so-called runner section 34b that is branched into four parts within the manifold block 22.
The portions adjacent to each of the gate holes 32a to 32d are pipe-shaped chips 36a, 36b, 36c, and 36d.
It is formed by. Each chip 36a-36
Around d are heating coils 38a, 38b, 38
The heating coils 36a to 38d are wound around the heating coils 38a to 38d, respectively, and when a high frequency current is passed through the heating coils 38a to 38d, each of the chips 36a to 36d generates heat, as will be described in detail later. The manifold block 22 is heated to a desired temperature by suitable heating means (not shown).

Similar to the conventional hot runner type injection molding apparatus, the molten resin injected from the nozzle of the molding machine passes through the resin passageway and is filled into each of the cavities 12a to 12d. Normally, the cavity plate 26 and the moving half 16 are cooled, and after the resin in each cavity 12a to 12d is cooled and solidified,
The moving half 16 is moved back and the mold is opened. At this time, the products formed in the cavities 12a to 12d are the cores 17a to 17 of the moving half 16.
17d and removed from the stationary half 14, but if the resin temperature near the gate holes 32a to 32d is too high, the resin may pull strings, causing a phenomenon called poor gate cutting, or the mold may open. During this time, the molten resin in the resin passage may leak out from the gate holes 32a to 32d. Conversely, if the temperature is too low, the resin near the gate holes 32a to 32d will solidify, making injection impossible in the next cycle. Therefore, the resin temperature near the gate hole must be maintained within a critical temperature range that is neither too high nor too low.

Each heating coil 38a to 38d is connected to a relay box 4.
High frequency power supply circuits 42 in series with each other via 0
connected to. The power supply circuit 42 includes a rectifier circuit 44 that rectifies alternating current from an AC power source and converts it into direct current (pulsating current), a switching element 46 that repeats opening and closing (on and off) under the control of a temperature control circuit 52, which will be described later, and a transformer. 48, a capacitor C connected in parallel to the primary side of the transformer 48, and a filter circuit 50.
The four heating coils 38a to 38d are located on the secondary side of the
are now connected in series. The temperature control circuit 52 is brought into contact with the tips of the chips 36a to 36d, respectively, and is connected to the tips of the chips 36a to 36d.
Four temperature sensors 54a, 54b, 54c, and 54d are provided for detecting the temperature at the tip of the tip 6d. The outputs of the four temperature sensors 54a to 54d are sequentially input to an amplification circuit 58 by a switching circuit 56, amplified, and then input to an A/D conversion circuit 60. Each sensor 54a to 54d is converted into a digital signal by this A/D conversion circuit 60.
The temperature information from is stored in the storage circuit 64 under the control of the control circuit 62. A set temperature input circuit 66 and a temperature display circuit 68 are further connected to the control circuit 62. A set temperature input circuit 66 inputs to the control circuit 62 the set temperature of the tip end selected by a setting dial or the like. This set temperature is stored in the storage circuit 64 under the control of the control circuit 62. The control circuit 62 stores the temperature information from each temperature sensor 54a to 54d that has been temporarily stored in the storage circuit 64, that is, the four chips 38a at that time.
- 38d are taken out, the average value of the temperatures of the tips of the four chips 38a-38d is determined by the arithmetic circuit 70, and the difference between the average value and the set temperature is determined. The control circuit 62 controls the oscillation circuit 72 according to the magnitude of this difference.
Change the output signal of 2. In the power supply circuit 42 in this embodiment, the lower the frequency within a predetermined range, the greater the power is applied to the heating coils 38a to 38d.
The control circuit 62 controls the oscillation circuit 72 so that the larger the difference between the set temperature and the average temperature of the chip tip, the lower the frequency.
control. In this embodiment, the oscillation circuit 72 is 20KHz.
Oscillates between ~50KHz. The output signal of this oscillation circuit 72 is current-amplified by a drive circuit 74 and is applied to the switching element 46 of the power supply circuit 42.
to drive. As this switching element 46 repeats opening and closing according to the oscillation frequency of the oscillation circuit 72, a high frequency current flows in the primary side of the transformer 48, a high frequency current is induced in the secondary side of the transformer 48, and the secondary side of the transformer 48 is induced. A high frequency current is supplied to the four heating coils 38a to 38d connected in series on the next side. When a high frequency current flows through the heating coils 38a to 38d, each chip 36a to 36d around which the heating coil is wound generates heat by electromagnetic induction. Of course, each of the chips 36a to 36d must be made of a material that can generate heat by high frequency induction heating. Various materials are known as such materials, but as is clear to those skilled in the art, each chip 36a to 36d must withstand high temperature and pressure, so the material is selected with these points in mind. must be selected. In particular, it is desirable to have high mechanical strength even when heated to high temperatures, high magnetic permeability, and low temperature dependence of magnetic permeability. Examples of such materials include SKD-61 and SKD-62 for hot molds. The temperature control circuit 52 repeatedly compares the average value of the actual temperature at the tip of each chip 36a to 36d input from each temperature sensor 54a to 54d with the set temperature, and if the former is lower than the latter, both are compared. The oscillation frequency of the oscillation circuit 72 is increased as the difference between the two becomes smaller. When this oscillation frequency increases, the transformer 4
The frequency of the current flowing through the primary side of the heating coils 38a to 38d also increases, and the frequency of the current supplied to the heating coils 38a to 38d also increases.
The power supplied to a to 38d becomes smaller. That is, when the actual temperature at the tip of the chip is lower than the set temperature, the temperature control circuit 52 applies a large amount of power to the heating coils 38a to 3 when the difference is large.
8d, and decreases the power supplied as the actual temperature approaches the set temperature, thereby converging the actual temperature of the tip end to the set temperature. Conversely, when the actual temperature exceeds the set temperature, the greater the difference, the greater the power supply is reduced to bring the actual temperature closer to the set temperature. The temperature display circuit 68 also displays the actual temperature at the tip end of the chip.
Displays the difference from the set temperature, etc. In the device of this embodiment that heats the chips by such high-frequency induction heating, the chips 36a to 36d themselves are heated, so compared to heating the taps by heat transfer from a resistance heater. Thermal response is fast and the chip temperature can be precisely controlled without delays caused by ringing or heat transfer.

FIG. 2 shows the structure around each chip in detail, taking the chip 36a as an example.

As shown in FIG. 2, the chip 36a is a pipe-shaped member having a through hole 80 forming a resin passage near the gate hole. The through hole 80 becomes narrower at the tip (on the gate hole 32 a side)
It has approximately the same diameter as a. Annular protrusions 82a, 82b are provided on both end surfaces of the chip 36a.
is provided. The chip 36a is pressed and held between the manifold block 22 and the cavity plate 26, and at this time, the protrusions 82a and 82b are deformed to some extent to prevent resin leakage from the pressing surface. It's getting old.
Of course, other sealing means such as an O-ring may be used to prevent resin leakage. In addition, the protrusion 82b on the tip surface reduces the contact area between the chip 36a and the cavity plate 26, and
It also helps to reduce the amount of heat taken away from the tip of the cavity plate 26 by the cavity plate 26. Chip 36a
A recess 84 into which the tip of the temperature sensor 54a is inserted is provided near the tip of the temperature sensor 54a. heating coil 38
a and the temperature sensor 54a are housed in a case 86 made of metal that has a high frequency shielding effect, and the lead wire 88a of the heating coil 38a and the lead wire 8 of the temperature sensor 54a
8b extends to the relay box 40 through a shield gap 90 integrally connected to the case 86. The heating coil 38a is made of a metal with good conductivity and resistance to corrosion, such as silver, a silver alloy, or a core wire such as copper wire, and an insulating coating placed over the core wire.
Depending on the size of the tip, it is usually wound around the tip in several to ten turns. Chip 36a
There is heat transfer from the manifold block 22 to the rear end, and conversely heat is taken away from the tip of the tip 36a by the cavity plate 26, so the heating coil 38a is as close to the tip 36a as possible.
The coil 38 is wound near the tip of the coil 38 at the tip.
It is desirable that the magnetic flux from a be concentrated.

The relay box 40 is connected to the high frequency power supply circuit 4
2, a connector 100 for connecting the secondary side of the transformer 48, and each of the heating coils 38.
Connector 101 for connecting a to 38d,
102, 103, and 104. Connectors 101, 102, 103, and 104 are connected to connector 100 in series. Furthermore, gate balance adjustment connectors 111, 112, 113, and 114 are connected to connect gate balance adjustment circuits (in parallel) so as to straddle each connector 101, 102, 103, and 104. This gate balance adjustment connector 111
By connecting appropriate gate balance adjustment circuits to the chips 36a to 114, the temperatures of the individual chips 36a to 36d can be controlled. FIG. 1 shows an example in which a capacitor 105 is connected in parallel to the heating coils 38a and 38c via gate balance adjustment connectors 111 and 113, respectively. In this case, the temperature of the chips 36a, 36c around which the heating coils 38a, 38c are wound increases,
The temperature of the chips 36b, 36d around which the other heating coils 38b, 38d are wound decreases. If a coil or resistor is used instead of a capacitor as the gate balance adjustment circuit, the heating coil 38
Chips 36a and 36c around which a and 38c are wound
temperature decreases, and the temperature of the other heating coils 38b, 38d decreases.
The temperature of the chips 36b and 36d around which the material is wound increases. In other words, by selectively connecting gate balance adjustment circuits such as capacitors, coils, and resistors in parallel to the heating coils, it is possible to change the distribution of power supply to each heating coil. a plurality of heating coils 38 connected to
Chip 36 generated by a to 38d
The temperatures of a to 36d can be raised and lowered separately. In other words, a capacitor may be connected to the corresponding gate balance adjustment connector so that a heating coil wound around a chip whose temperature tends to drop due to some factor receives more power than other heating coils. , conversely, the power supplied to the heating coil wrapped around the chip whose temperature is more likely to rise than others due to some factor is smaller than the power supplied to other heating coils, so that the power supplied to that heating coil is adjusted accordingly. A coil or resistor may be connected to the gate balance adjustment connector.

Needless to say, the effect of the gate balance adjustment circuit increases as the value of the element increases. Therefore, the operator may check the temperature display or check the state of the resin in each gate hole and connect the element with the appropriate value to the appropriate gate balance adjustment connector, or the operator may connect the element with the appropriate value to the appropriate connector for gate balance adjustment. Gate balance adjustment circuits having a plurality of values may be provided for each heating coil so as to be freely switchable, and an element having an appropriate value may be selected and connected in accordance with the temperature difference between chips.

Further, as shown in FIG. 3, the switching may be performed automatically under the control of a control circuit 62. That is, in the relay box 40a shown in FIG. 3, each gate balance adjustment connector is a relay 121, 122 having six fixed contacts and one movable contact that is selectively brought into contact with one of the six fixed contacts. , 123, 124. Five of the six contacts of each relay 121 to 124 are connected to capacitors of different values, and the remaining one contact is open. Each relay 121 to 124 is a relay drive circuit 1 controlled by the control circuit 62.
25. The control circuit 62 selectively drives the relays 121 to 124 according to the temperature variations of the four chips 36a to 36d input from the temperature sensors 54a to 54d, and connects the corresponding heating coils 38a to 124 to the capacitors of a desired value. The relay drive circuit 125 is controlled to be connected in parallel to 38d.

The present invention has been described above using an example in which a capacitor is used as a gate balance adjustment circuit, but as mentioned above, a coil and a resistor can also be used as a gate balance adjustment circuit, and these three They may be used in any appropriate combination.

Note that the lead wires passed through the mold cannot be made too thick for practical purposes, but in order to minimize the resistance loss including the skin effect of the line from the power supply circuit to the coil, the line up to the relay box 40 is It is desirable to use a thick conducting wire with as little high frequency resistance as possible, and to place the relay box 40 as close to the mold as possible.

Further, in the above embodiment, a commutation type circuit in which the supplied power increases as the frequency becomes lower is used as the high frequency power supply circuit 42, but a deflection type circuit in which the supplied power increases as the frequency increases is also used. I can do that. Further, in the embodiment, the temperature control circuit 52 includes four chips 36a to 3.
Although the average value of the actual temperature at the tip of the chip 6d is compared with the set temperature, the actual temperature at the tip of any one tip may be compared with the set temperature.

(Effects of the Invention) As explained in detail above, in the device of the present invention, due to the design of the mold, etc., there is a difference in heat transfer between the plurality of gate holes, so that the power is distributed uniformly to each heating coil. Even in the case where the so-called gate balance is lost due to variations in the temperature of the gate hole by supplying the heating coil, it is possible to maintain a good gate balance by changing the power distribution to each heating coil.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an injection molding apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view showing a part of the apparatus shown in FIG. 1 in detail, and FIG. FIG. 3 is a diagram showing the main parts. 12a-12d...Cavity, 32a-32
d...Gate hole, 36a-36d...Chip, 3
8a to 38d... Heating coil, 42... High frequency power supply circuit, 52... Temperature control circuit, 100 to 1
04... Connector, 105... Capacitor,
111-114...Connector for gate balance adjustment, 121-124...Relay, 125...Relay drive circuit.

Claims (1)

[Claims] 1 Consisting of a stationary half and a movable half, a plurality of cavities formed when both halves are closed, each cavity connected to a nozzle of a molding machine, and an opening in each cavity. a mold having a resin passageway for supplying molten resin into each cavity from a gate hole in which the resin is melted, and a heating means for heating the resin passageway of the mold to keep the resin in the resin passageway in a molten state. In the hot runner injection molding apparatus, at least a portion of the resin passage near each gate hole is formed of a pipe-shaped member made of a material that can be heated by high-frequency induction heating, and the heating means A plurality of high-frequency induction heating coils wound around each pipe-shaped member and connected to each other in series, high-frequency power supply means for supplying high-frequency power to the high-frequency induction heating coils, and connected in parallel to each of the high-frequency induction heating coils. gate balance adjustment circuit connection means provided corresponding to each of the heating coils for connecting a gate balance adjustment circuit that changes power distribution to the heating coils; A molding apparatus comprising a temperature control means for controlling the temperature of the pipe-shaped member to a desired value by controlling the electric power supplied to the induction heating coil. 2. The frequency of the high-frequency power supplied to the high-frequency heating coil by the high-frequency power supply means is
The molding apparatus according to claim 1, characterized in that the frequency is 20KHz to 50KHz. 3. The molding apparatus according to claim 1 or 2, wherein the gate balance adjustment circuit includes a capacitor. 4. The molding apparatus according to claim 1 or 2, wherein the gate balance adjustment circuit includes a coil. 5. Claim 1 or 2, wherein the gate balance adjustment circuit includes a resistor.
The molding device described in Section 1.