JPH0713913B2 - High frequency heating coil and heating method using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heating coil for heating a mold using high frequency.

[Conventional technology]

Conventionally, a method and an apparatus for heating a mold used for plastic injection molding using a high frequency is as described in JP-B-43-17815 and JP-B-58-40504. And a high-frequency oscillator and a heating coil, and the heating coil has a similar shape to the surface shape of the mold on which the surface of the molded product is to be formed. After opening the mold, a heating coil is inserted into the mold to oscillate a high frequency to sequentially heat the mold surface on which the surface of the molded product is to be formed.

Further, Japanese Patent Application Laid-Open No. 50-45039 proposes a method in which a heating coil is provided inside the die and the die is heated by a heating coil provided in the die at the time of molding.

[Problems to be Solved by the Invention]

However, in the above-mentioned prior art, in order to uniformly heat the mold forming the molded article or the entire mold surface, the shape of the heating coil is similar to the shape of the mold surface facing the coil, and the mold is used at high frequency oscillation. By maintaining a uniform air gap between the die surface and the coil, the eddy current generated on the die surface is made uniform and the Joule heat generated by the eddy current is made uniform.

For this reason, when the mold surface has a sliding structure such as an outer slide, an inner diameter slide, and a slide for protruding the formed product, or when the mold is composed of a combination of several parts, The current is concentrated in the slide sliding part and the part combination part, spark discharge occurs, and there is a defect that seizure occurs in the mold and galling occurs during sliding motion.

Therefore, if a part of the mold has a slide part or a part matching part, the discharge phenomenon due to the concentration of eddy current due to the contact state between the molds in the clearance part or the fitting part is not completely inevitable. It was not there.

The present invention has been made in view of the above problems of the prior art, and provides a method and a high-frequency heating coil having a novel structure capable of performing stable heat treatment without causing discharge due to concentration of eddy currents. Is.

[Means for Solving the Problems]

The present invention relates to a mold for a resin injection molding apparatus, and more particularly to a coil for heating a cavity core member and a method for heating a mold member using the heating coil. The heating coil has a shape such that an air gap a between the coil and the cavity core, an air gap c between the piece member, and an air gap b between the base mold. And the relationship between the air intervals a, b, c is that the relationship of a <c <b is established.

That is, the invention of claim 1 of the present invention is to heat the cavity core of the injection-molding die and the constituent members of the die (the die members 2, 2, An object of the present invention is to provide a high-frequency coil capable of solving a problem such as seizure caused by heating of the bridge members 4, 4). The present invention relates to the shape of the heating coil between the coil and the cavity core. There is an air space a, an air space c between the bridge member and an air space b between the base mold, and the relationship between the air space distances a, b, c is a <c By satisfying the relation of <b 2, the heat from the high frequency coil can be efficiently transferred only to the cavity core.

In the present invention, the mold member that forms the molded product is a mold member that can be used for injection molding, compression molding, etc. of plastics, and its shape, size, etc. are set as desired and are not limited in any way. Is. Any material can be used as long as it can be heated by generating an induced current by high frequency. Usually, the mold is composed of a plurality of members, for example, a cavity core that forms the surface shape of the molded product,
Duck piece supporting the cavity core, and the cavity core,
It consists of a base mold etc. that supports the duck piece and has a cooling water channel, all of which are called molds. In the present invention, the mold member that forms the molded product is used to form the molded product. It means a member that requires heating, and in the above example, it means a cavity core, but it does not necessarily have to be a member having a surface with which a molded product contacts.

In the present invention, the surface of the mold member facing the high-frequency heating coil means a high-frequency action directly from the high-frequency heating coil arranged for heating the member before injecting a plastic material or the like into the mold member. Receiving the surface that produces the conductive flow, and heating the mold member includes heat treatment in all steps of heating the mold member with a high-frequency heating coil, and heating the member immediately before forming a molded product. Not only the surface quenching treatment of the die member is included.

Further, in the present invention, the joining portion and the sliding portion appear on the surface of the die member facing the high-frequency heating coil, and the member which is in contact with the joining portion, the sliding portion and the die member. Other than the above, it includes a joint portion with a die portion and a sliding portion. Further, the joint portion refers to a combined portion of the die members, a joint portion between the die member and another portion, a contact portion between upper and lower die members, and the sliding portion refers to an outer slide, an inner diameter slide of the die member, It refers to a slide portion such as a pin for ejecting a molded product, a slide portion with another portion that comes into contact with the mold member when it is driven, and the like.

The air gap between the high-frequency heating coil and the mold member means an average distance from a position of a surface of the mold member facing the coil to the coil, and in the present invention, the air gap is partially defined. To be large means that the interval is basically almost constant and is partially large. The phrase "generally constant" means that the working surface of the high-frequency heating coil and the mold member facing the working surface are substantially similar in shape and are arranged at substantially constant intervals. That is, where b is the air space between parts other than the mold member that do not require heating, a is the space between the mold members that require heating, and c is the space between the joints or sliding parts, then a <c <b The shape of the high frequency heating coil is set so that

Here, the air gap is represented by an average distance because this is because the influence of the magnetic field due to the high frequency at a certain position of the mold member is the integrated average of the magnetic fields generated in the entire high frequency heating coil, and the average distance is large. Then, the influence of the magnetic field on that portion of the mold member is reduced, and therefore the magnitude of the induced current generated is reduced. That is, when a high frequency is applied to a high frequency heating coil (hereinafter simply referred to as a coil), a magnetic field according to the primary current flowing in the coil is generated around the coil, and the magnetic field causes an induced current on the surface of the mold member. The mold member causes Joule heat generation of I ² R (I: current, R: resistance) due to the generated induced current and the electric resistance of the mold member, and the surface temperature rises. At this time, the air gap (A) between the coil and the surface of the mold member and the induced current (I) generated in the mold are (K = coefficient determined by high-frequency oscillator frequency, output, and mold member material characteristics). Therefore, the larger the air gap between the heating coil and the mold member, the mold member surface temperature. Is less likely to rise.
Therefore, it is possible to reduce the induced current generated by increasing the air gap in the joint portion and the sliding portion, and as a result, it is possible to prevent the occurrence of discharge, burn-in and the like.

How much the air gap is set depends on the value of k, that is, the frequency of the high-frequency oscillator, the output, the characteristics of the mold member material, the bonding state of the bonding portion and the sliding portion, and the like. The heat treatment is performed so that the phenomenon such as discharge does not occur. That is, by setting the air gap according to the desired heat treatment, it is possible to sufficiently raise the temperature of the necessary portion of the die member itself and to suppress the temperature rise in the joint portion and the sliding portion. Is. Generally, the air gap at the joint and the sliding portion becomes larger when the wavelength of the high frequency is small, the output is large, the volume specific resistance of the mold member material is large, and the adhesion between the joint and the sliding portion is poor, If it is the other way around, it can be relatively small.

Note that other configurations for heat-treating the mold member using the coil according to the present invention may be based on known techniques.

〔Example〕

Next, a specific coil shape will be described with reference to examples.

FIG. 1 shows a first embodiment of the present invention, in which FIG.
Is a high-frequency heating coil, 2 is a base mold, 3 is a cavity core (mold member) provided with a surface for forming a molded product, 4 is a scrap piece for storing the cavity core in the mold, and 5 is a scrap piece. Cavity cores that perform sliding movements, 6 indicates a combined surface (joint portion) of the cavity cores and duck pieces, and 7 indicates a sliding surface (sliding portion) between the cavity cores and duck pieces that perform sliding movement.

FIG. 2 is a perspective view of the high frequency heating coil 1 of FIG.

Here, the air gap a between the coil action part and the cavity core a
And a ', the air gaps b and b'of the base mold except for the acting portion of the coil, and the air gaps c and c'of the coil and the joint portion and the sliding portion are a <c <b and a'<, respectively. c '<
b '. In this way, by increasing the air gap between the mold combination part 6 and the mold sliding surface 7 with the coil, the induction current in the combination part and the sliding part is reduced during high frequency heating, and discharge and baking are performed. It is possible to prevent the occurrence of sticking.

FIG. 3 shows the mold member surface temperature when heated by the apparatus shown in FIG. As shown in FIG. 3, the surface temperature of the die member is reduced even though the temperature at the combined portion is lowered (the induced current is reduced) by increasing the air gap between the coil and the die member. Can be raised sufficiently.

FIG. 4 is a schematic plan view showing another embodiment of the present invention.
In FIG. 4, 41 is a coil, 42 is a die member, and 43 is a die combination portion (joint portion).

FIG. 5 is another embodiment of the present invention, and is a schematic side view when the surface of a cylindrical mold member is quenched. In FIG. 5, 51 is a coil, 52 is a die member, and 53 is a combination part.

The mold member surface temperature distribution shown in FIG. 3 was obtained under the following conditions.

a = 2mm, b = 30mm, c = 20mm, high frequency 10KHz, output 10Kw, cavity core electric resistance 50μΩ ・ cm.

〔The invention's effect〕

As described above, the present invention includes at least a pair of cavity cores 3, 5, base molds 2, 2 for supporting the cavity cores, and piece members 4, 4 for holding the cavity cores in the base molds. The heating coil has an air gap a between the coil and the cavity core, an air gap c between the bridge member, and an air gap b between the base mold. The air spacing a, b,
The relationship of c is the seizure when the mold is heated at a high frequency by heating only the cavity core to the molding required temperature within the energization time of the heating coil in which the relationship of a <c <b is established, The galling is prevented, and as a result, the durability of the mold can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a mold member heat treatment using the coil of the present invention, FIG. 2 is a schematic perspective view of the coil shown in FIG. 1, and FIG. 3 is shown in FIG. Mold member surface temperature diagram, FIG. 4 and FIG. 5 are a schematic plan view and a schematic side view showing another embodiment, respectively. 1,41,51 …… Coil, 2 …… Base mold, 6,43,53 …… Joint part, 3,5 …… Cavity core, 4 …… Duck piece, 7 ……
Sliding parts, 42, 52 ... Mold members.

Claims (2)

[Claims] 1. A heating coil for heating a mold member for molding a molded article by injecting a plastic material by using high frequency, wherein the mold member is at least a pair of cavity cores 3,5.
A mold 2,2 for supporting each of the cavity cores, and a piece member 4,4 for holding the cavity core in the base mold, and the shape of the heating coil is the coil. The air gap a between the cavity core and the cavity member, the air gap c between the bridge member, and the air gap b between the base mold and the air gaps a, b, and c. The relationship is a high-frequency heating coil for heating a die member, characterized in that the relationship of a <c <b is established. 2. At least a pair of cavity cores 3, 5, and
Molds 2 and 2 for supporting the cavity cores, and piece members 4 and 4 for holding the cavity cores in the base mold, and heating and closing the cavity cores to inject resin. In a method of heating a die member for forming a molded article by means of an air gap a between the coil and the cavity core, an air gap c between the piece member and the base die. Has an air gap b, and each of the air gaps a, b, c
The relationship of a <c <b is established, and only the cavity core is heated to a molding required temperature within a time period in which the coil is energized. How to heat a member.