JP3087083B2 - Graphite mold for plastic molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for plastic molding, and more particularly to a graphite mold for plastic molding in which the mold is formed of a graphite material.

[0002]

2. Description of the Related Art To mold a product having a predetermined shape from a plastic material, whether injection molding or vacuum molding, a so-called cavity is generally formed by a divided mold as shown in FIG. Plastic products are formed according to the shape of the product. In this molding, taking a thermoplastic plastic as an example, the plastic material is heated to its plasticizing temperature (generally 175 ° C. to 320 ° C.), molded in a mold, and then cooled. Must be solidified. The applicant has advantages of such a plastic molding die that the thermal expansion is extremely small, so that accuracy in plastic molding can be easily obtained, and that the heat radiation characteristics are very good and the plastic molding can be performed efficiently. There has already been proposed a plastic molding die in which the cavity forming die is made of graphite by making effective use.

By the way, even if a mold forming a cavity is formed by such graphite, a spool bush for injecting a heated plastic material into the cavity, an ejector pin for releasing a plastic molded product, and a mold. Conventional structural materials such as carbon tool steel SK4, alloy tool steel SKD61, or high-speed tool steel SKH51 are used for structural components of a mold such as a nest for partially reinforcing the cavity surface. It was being done.

[0004] The steel material constituting the above components has a coefficient of thermal expansion that is 2 to 6 times that of the graphite of the mold material constituting the cavity. That is, the thermal expansion coefficient of a general graphite material is 2.0 × 10 ^{−6 /} ° C. to 7.0 × 1.
The thermal expansion coefficient of the steel material is as high as 12.9 × 10 ⁻⁶ / ° C. (at about room temperature) while it is 0 ⁻⁶ / ° C. (at 50 ° C. to 400 ° C.). In addition, these structural parts need to be assembled with a very small clearance to a graphite mold in order to prevent the occurrence of burrs on plastic molded articles and to perform molding more precisely. .

For this reason, in a conventional graphite mold for plastic molding, when heat from a plastic material that is heated and injected into the mold is transmitted to each structural part, the structural parts are heated more than a graphite mold. Will inflate,
Naturally, the clearance with the graphite side is lost. In such a state, the graphite side may be compressed or the like, causing cracks. In particular, for structural parts such as ejector pins, for example, the sliding contact with the graphite mold side is repeated, so that galling occurs and further cracks and cracks are more likely to occur on the graphite mold side due to resin entering the abraded part. Many will occur.

The present inventors have conducted various studies on how to prevent cracks and cracks from occurring in such a graphite mold, and as a result, completed the present invention. .

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to address the above-described situation in this type of graphite mold for plastic molding, and the problems to be solved are as follows.
Cracks or cracks caused in a graphite mold by foreign structural components.

The object of the present invention is to:
An object of the present invention is to provide a graphite mold for plastic molding that does not cause cracks or cracks.

[0009]

To solve SUMMARY and operation for solving the above problems, firstly, to describe a reference numeral used in real施例, in graphite mold 10 for plastic molding, a spool bush constituting the mold Structural components such as 13, ejector pins 14, and inserts 15 were formed of a material such as metal or ceramic having a thermal expansion coefficient equal to or less than that of the graphite constituting the mold .

In the graphite mold for plastic molding 10 configured as described above, the thermal expansion coefficients of the structural components such as the spool bush 13 and the ejector pin 14 are different from those of the graphite forming the movable mold 11 and the fixed mold 12. Since the plastic molding graphite mold 10 is heated by the plastic material injected into the cavity C from the nozzle 20 through the spool bush 13 because the plastic molding mold 10 is equal to or less than that, the movable mold 11 made of graphite is used for each structural component. Or, it does not thermally expand beyond the fixed mold 12. Therefore, the clearance between the movable mold 11 or the fixed mold 12 and each structural component does not disappear, and the movable mold 11
Also, the graphite forming the fixed mold 12 does not crack or crack.

In order to solve the above-mentioned problem,
Means taken of the Invention According to the first one to three請 Motomeko is the thermal conductivity of the structural components constituting the plastic molded graphite mold 10 according to the first claim, the movable mold 11 and the stationary mold 12 That is, it is equal to or higher than the constituting graphite.

[0012] In this plastic molding graphitic 10 of the to a one to three請 Motomeko, those graphite equal to or more the thermal conductivity constituting the movable mold 11 and fixed mold 12 in each structural component Has the following effects. That is, the entire graphite mold 10 for plastic molding is moved from the nozzle 20 to the spool bush 1.
3, even if heated by the plastic material injected into the cavity C through the respective structural parts 3, the heat is transferred to graphite such as the movable mold 11 and the fixed mold 12 adjacent to each other,
Alternatively, since the electric power is quickly transmitted to the outside of the system via a member (not shown) supporting these structural parts, the temperature of each structural part does not become higher than that of the movable mold 11 or the fixed mold 12. Therefore, even in this respect, the structural components do not thermally expand more than the movable mold 11 and the fixed mold 12, and the movable mold 11 and the fixed mold 12 do not crack.

[0013] Particularly, in the plastics molding graphitic 10 according to this configuration one to three請 Motomeko, the respective structural parts themselves have a sufficient thermal conductivity, rapidly heat through the manufacturing component As long as it can be taken out of the system, the thermal expansion coefficient of each structural component itself may be larger than that of graphite. Needless to say, if the coefficient of thermal expansion of each structural component itself is defined in the same manner as the graphite mold for plastic molding 10 according to the first claim, the graphite mold without cracks and cracks will be sufficient. .

[0014]

EXAMPLES Next, described with reference to the embodiment shown each invention with reference to the drawings.

Embodiment 1 FIG. 1 shows a cross section of an injection molding machine employing a graphite mold for plastic molding 10 according to the first to third claims, and the graphite mold for plastic molding 10 is made of graphite. The movable mold 11 and the fixed mold 12 are abutted to form a cavity C for performing plastic molding. For this cavity C,
A plastic material is injected from a nozzle 20 shown in the upper part of the figure through a spool bush 13 provided in the fixed die 12.

Further, the graphite mold 10 for plastic molding is used.
In the above, the fixed mold 12 is fixed to a stand or the like (not shown) and supported, and the movable mold 11 can be moved left and right with respect to the fixed mold 12. Since the movable die 11 needs to form the cavity C in a constant state while always accurately maintaining the position of the movable die 11 with respect to the fixed die 12, the movable die 11 and the fixed die 12 have a structure. It is a kind of part. The graphite mold 10 for plastic molding also has other structural parts such as the ejector pins 14 and the inserts 15 which are required as other molding dies, but these are usually required as molds. Therefore, the description is omitted.

In the first embodiment, the spool bush 13, the ejector pin 14, the insert 15 and the structural parts supporting the same have a thermal expansion coefficient of 4.6.
× 10 ⁻⁶ / ° C. (at 30 to 300 ° C.) -42% iron
A nickel alloy, a so-called 42 alloy material, was used. On the other hand, graphite constituting the movable mold 11 and the fixed mold 12 includes:
The thermal expansion coefficient and the thermal conductivity are 5.0 × 10 ⁻⁶ /
° C (at 30-300 ° C) and 80 kcal / m
hr ° C was used.

Embodiment 2 In this embodiment 2, the thermal expansion coefficient is 3.6 × 10 ^-6.
/ ° C (at RT-1000 ° C), thermal conductivity 240
Aluminum nitride of kcal / m · hr ° C. was used. on the other hand,
The graphite constituting the movable mold 11 and the fixed mold 12 has a thermal expansion coefficient and a thermal conductivity of 4.5 × 10 ⁻⁶ each.
/ ° C (at RT-400 ° C) and 120 kcal /
m · hr ° C. was used. Other configurations are the same as those in the first embodiment.

Not limited to the case of this embodiment, it is natural that metal materials, ceramics and the like other than those of the embodiment can be adopted as a material constituting each structural component such as the ejector pin 14 and the like. In this case, it is needless to say that the thermal expansion coefficient and the thermal conductivity of the graphite forming the movable mold 11 and the fixed mold 12 can be within the above-mentioned specified ranges. This is very important.

[0020]

As described above, according to the present invention, or not a, the thermal expansion coefficient of each structural component, it is equivalent to that or less than the the fact to the feature of the graphite forming the movable mold 11 and the stationary mold 12 Thereby, even if heat from the plastic material is applied, it is possible to provide a graphite mold for plastic molding that does not cause cracking or cracking.

Further, in the first to third aspects of the present invention, the thermal conductivity of each structural component is determined by the movable mold 11 and the fixed mold 1.
Since it is made equal to or larger than that of the graphite constituting No. 2, the same effect as above can be surely realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a typical example of an injection molding machine employing a graphite mold for plastic molding according to each invention.

[Explanation of symbols]

 10 Graphite mold for plastic molding 11 Movable mold 12 Fixed mold 13 Spool bush 14 Support pin 15 Guide bush

Claims (3)

(57) [Claims] In a graphite mold for plastic molding, a spool bush constituting the mold is made of metal or ceramic.
And the thermal conductivity of the graphite type graphite
Plus that is equal to or more than
Graphite mold for molding tics. 2. A graphite mold for plastic molding, wherein an ejector pin constituting the mold is made of metal or ceramic.
And the thermal conductivity of the graphite type graphite
Plus that is equal to or more than
Graphite mold for molding tics. 3. A graphite mold for plastic molding, wherein a nest constituting the mold is made of a metal or ceramic material.
If the thermal conductivity of the material is equal to that of the graphite type graphite,
Or plastic molding characterized by more
For graphite type.