JPH08127024A - Meterial feed method for injection molding device and charge hopper - Google Patents

Abstract

PURPOSE: To feed a mixture of a plurality of materials of different physical properties in a uniformly dispersed state by storing the mixture into a charge hopper section with a specified angle or more angle on a horizonatal surface on the outside of a side wall and feeding the mixture from its lower end opening. CONSTITUTION: A mixture M, prepared by mixing injection molding materials of two kinds or more of different physical properties mixed in a mixer 13 for a given time and dispersed uniformly, is manufactured and free fallen into a sotrage section 22 of a charge hopper 20, and the mixture M is fed from a lower end opening 27 into an injection molding device 1. The lower end opening 27 of the charge hopper 20 is of the same diameter as a material feed opening 1a of the injection molding device 1 or of smaller diameter, while an upper end opening 26 is of the same diameter as a material discharge outlet 13a of the mixer 13 or of a larger diameter, and the angle formed by the inner face and the horizontal surface of a side wall is set to cover from the upper end to the lower end of the whole periphery of the side wall, and the angle on the horizontal surface on the outside of the side wall is set to be 60 deg.C or more. The friction resistance of the mixture M at the time of free falling is less by the arrangement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to specific gravity, shape, size,
Suitable for a material supply method of an injection molding apparatus, a material supply method of an injection molding apparatus, and other molding apparatuses for temporarily storing and supplying a mixture obtained by mixing two or more kinds of materials having different physical properties such as surface roughness Regarding charge hopper.

[0002]

2. Description of the Related Art Generally, in an injection molding apparatus, a technique of crushing a molding portion corresponding to a runner or a gate removed from a molded product and reusing it as a recycled pellet has been widely used. Usually, the material supply to the injection molding device is
First, one batch of natural pellets, recycled pellets, and pigment master pellets were weighed and supplied to a paddle-type mixer by air transportation or the like, mixed for a certain time in the mixer, and then uniformly dispersed. A mixture composed of a plurality of materials is supplied by being dropped from a mixer to a charge hopper of an injection molding device. Further, in order to increase the strength of the molded product, glass fiber or the like may be mixed in the molding material.

Further, in general, the charge hopper prevents the size of the injection molding apparatus from increasing in the vertical direction.
The peripheral wall is formed in a conical shape that shrinks downward, and the inclination angle of the peripheral wall with respect to the horizontal plane is set so that the molding material stored in the charge hopper is supplied in order from the charged material. In consideration of angles and the like, the angle on the horizontal plane outside the peripheral wall is set to be smaller than 60 °.

[0004]

However, as described above, a mixture of a plurality of materials having different physical properties, for example,
When the mixture of the round pellets and the cylindrical pellets is supplied to the charge hopper, the variation in mechanical strength of the molded product becomes large, and the problem that defective products occur more frequently occurs.

The present applicant conducted the following test to verify the above problem. As a molding material, glass fiber-containing cylindrical pellets (length: 10 mm, ash content: 42.9%) were 50.0% (setting is 1500 g, actually 50.01%).
7%), round pellets 49.0% (setting is 1470 g
Actually, 49.016%), pigment master pellets (ash content: 35%) 1.0% (setting 1% is 29g as instructed, 0.967%), and the paddle type mixer The material was continuously mixed in, and while the remaining amount of the molding material was detected by the level sensor in the tank, the material was intermittently introduced into the hopper of the injection molding device from the mixer.

A standard screw head, a shut-off valve, and a nozzle diameter of 4φ were used as the injection molding device, and the screw rotation speed was 60 rpm as molding conditions.
There was no back pressure, and the weighing was set to 100 mm (about 700 g per shot). Next, the molding method will be described. The first three shots were discarded. Next, one shot of TPGI was molded with a weight of 25 mm, and the test piece No. It was set to 1. In the next three shots, the ash content was measured. 1 to No. Three
It was a purged product. Next, by repeating the above, a sample for 10 shots of the test piece and a sample for 27 shots of the purged product were obtained. In addition, the measurement accuracy is 1500 g ± 3 g for the cylindrical pellet,
The round pellets were 1470 ± 6 g and the pigment master pellets were 29 g ± 1 g.

Then, the ash portion of the purged product was measured, and the specific gravity of the test piece, the notched Izod and the tensile strength were measured, and the test results of Tables 1 and 2 were obtained. However, the theoretical value of the ash content of the purged product is 21.78%.

[0008]

[Table 1]

[0009]

[Table 2]

It can be seen from Tables 1 and 2 that the variations in ash content, specific gravity, Izod and tensile strength are all large, and the quality of the molded product is deteriorated. The Applicant further conducted various tests to find out the cause of the above-mentioned problems, and found that the cause was due to the classification of the material in the charge hopper. In other words, due to the difference in the friction coefficient between the inner surface of the peripheral wall of the charge hopper and the material, the round pellets fall faster than the cylindrical pellets, the ratio of the round pellets at the bottom of the charge hopper increases, and the pellets are charged into the charge hopper. Due to the sequential accumulation of the mixture in a mountain shape, the ratio of easily rolled round pellets becomes higher at the bottom of the pile of the mixed mixture, and the ratio of hard-to-roll cylindrical pellets becomes higher at the top of the pile of the deposited mixture. As a result, it was found that the materials uniformly mixed in the mixer were classified in the charge hopper. The above classification phenomenon also occurs in the process of supplying (discharging) the mixed and stored materials from the charge hopper to the molding device. Round pellets that roll easily are also fed earlier than cylindrical pellets that roll less easily. As a result, the classification is further amplified. An object of the present invention is to provide a material feeding method and a charge hopper for an injection molding apparatus capable of feeding a mixture in which a plurality of materials having different physical properties are mixed in a uniformly dispersed state.

[0011]

According to a first aspect of the present invention, there is provided a material supply method for an injection molding apparatus, wherein two or more kinds of injection molding materials having different physical properties such as specific gravity, shape, size and surface roughness are mixed by a mixer. The mixing step of mixing for a certain period of time to obtain a uniformly dispersed mixture, the mixture in the mixer, the lower end opening has the same diameter as the material supply port of the injection molding apparatus or smaller than the material supply port, and The upper end opening has the same diameter as the material discharge port of the mixer or a larger diameter than the material discharge port, and the angle between the inner surface of the side wall and the horizontal surface is from the upper end to the lower end of the entire side wall to the outside of the side wall. At an angle on the horizontal plane at 60 °
It is provided with a supply step of allowing the mixture housed in the charge hopper to fall freely into the accommodating part of the charge hopper set above and temporarily accommodated therein, and to supply the mixture housed in the charge hopper from the lower end opening to the injection molding device.

The charge hopper according to claim 2 is connected to the material discharge port of the mixer and is discharged from the mixer by two or more kinds of materials having different physical properties such as specific gravity, shape, size and surface roughness. A charge hopper having a storage portion for temporarily storing the mixture, wherein the upper end opening of the charge hopper is set to the same size as the material discharge port of the mixer or a size surrounding the material discharge port, and the charge is performed. The angle formed between the inner surface of the side wall forming the accommodating portion of the hopper and the horizontal plane is set to 60 ° or more on the horizontal plane outside the side wall from the upper end to the lower end of the entire side wall.

Here, as in claim 3, the side wall is arranged in a substantially vertical direction, and as in claim 4, the side wall of the charge hopper is made of a transparent member,
A coating layer having a small friction coefficient is formed on the inner surface of the side wall of the charge hopper as in claim 5, and the mixture housed in the charge hopper is a mixture of molding materials as in claim 6. The lower end opening of the charge hopper is connected to the material supply port of the molding apparatus, and the lower end opening of the charge hopper is configured to have the same diameter as the material supply port of the molding apparatus or a diameter smaller than the material supply port. As described above, it is a preferred embodiment that the mixture is intermittently supplied from the mixer to the charge hopper by a constant amount.

[0014]

In the material supplying method for the injection molding apparatus according to the first aspect, in the mixing step, two or more kinds of injection molding materials having different physical properties are mixed for a certain time by a mixer,
Produce a uniformly dispersed mixture, and in the feeding process, let the mixture in the mixer freely fall into the storage part of the charge hopper to temporarily store it, and then store the mixture stored in the charge hopper from its lower end opening. It will be supplied to the injection molding machine. In the charge hopper, the lower end opening has the same shape as the material supply port of the injection molding apparatus or a smaller diameter than the material supply port, and the upper end opening has the same diameter as the material discharge port of the mixer or a larger diameter than the material discharge port. In addition, the angle between the inner surface of the side wall and the horizontal plane is set to 60 ° or more on the horizontal plane outside the side wall from the upper end to the lower end of the entire circumference of the side wall. The frictional resistance between the mixture and the side wall of the charge hopper during the free fall of the mixture supplied to the mixture is reduced. Further, when feeding from the charge hopper to the molding device, the conical portion is formed at an extremely large angle of 60 degrees or more, and the friction conventionally generated in the conical portion is greatly reduced or almost disappears. Since it has become, it will no longer cause classification. Therefore, the particles can be supplied in the state of particle size distribution in the charge hopper or in a mixed state, and a uniform product without segregation can be obtained.

In the charge hopper according to the second aspect, the upper end opening of the charge hopper is set to be the same as the material discharge port of the mixer or sized to surround the material discharge port, and constitutes the accommodating part of the charge hopper. The angle between the inner surface of the side wall and the horizontal plane is 6 at the angle on the horizontal plane outside the side wall from the upper end to the lower end of the entire side wall.
Since it is set to 0 ° or more, the frictional resistance between the mixture and the side wall of the charge hopper is reduced when the mixture supplied from the mixer into the charge hopper falls freely.

In the charge hopper according to the third aspect, since the side wall of the charge hopper is arranged in a substantially vertical direction, the mixture supplied from the mixer into the charge hopper can be mixed with the mixture at the time of free fall. The frictional resistance between the side walls of the charge hopper can be minimized. In the charge hopper according to the fourth aspect, since the side wall of the charge hopper is made of a transparent member, it is possible to visually confirm the remaining amount of the mixture with respect to the charge hopper.

In the charge hopper according to the fifth aspect, since the coating layer having a small friction coefficient is formed on the inner surface of the side wall of the charge hopper, it is possible to further reduce the frictional resistance between the mixture and the side wall of the charge hopper. It will be possible. In the charge hopper according to the sixth aspect, it becomes possible to reduce the frictional resistance between the side wall of the charge hopper and the mixture made of a plurality of types of molding materials such as natural pellets, recycled pellets and glass fiber-containing pellets.

In the charge hopper according to the seventh aspect, since the mixture is intermittently supplied from the mixer to the charge hopper in a constant amount, the constant amount of the mixture supplied from the mixer is regarded as one lump. It is possible to supply to the charge hopper, and it is possible to more effectively prevent classification of the mixture due to differences in rolling friction.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is a case where the present invention is applied to a method of supplying a molding material to an injection molding apparatus and a charge hopper used for the method. First, a material supply device 10 for supplying a molding material to the injection molding device 1.
The overall configuration of will be described. As shown in FIG. 1, the material supply device 10 basically includes a measuring unit 11 for measuring a molding material, a mixing unit 12 for mixing a molding material, and a measuring unit 1.
The blower unit 14 supplies the molding material measured in 1 to the mixer 13 of the mixing section 12.

The measuring unit 11 has four storage tanks 15 for storing natural pellets, recycled pellets, pigment master pellets, etc. as molding materials, a weighing hopper 16 disposed below the storage tank 15, and a weighing hopper 16. The weighing unit 11 is provided with a load cell 17 for measuring the weight of the hopper 16, and while the weight of the weighing hopper 16 is measured by the load cell 17, the slide damper 18 at the lower end of the storage tank 15 is sequentially opened and closed. A batch (for example, 3 kg) of molding material is weighed and stored in the weighing hopper 16. In addition, as the molding material, a material in which glass fiber, foam material or the like is mixed may be used.
Reference numeral 16a is a non-contact nozzle.

As shown in FIGS. 1 to 3, the mixing section 12 is provided between the mixing machine 13 such as a paddle type for mixing the plural kinds of molding materials, and between the mixing machine 13 and the injection molding apparatus 1. A charge hopper 20 is provided, and in the mixing section 12, the molding material in the measuring hopper 16 pneumatically transported by the blower unit 14 is mixed in the mixer 13 for a certain period of time so that a plurality of kinds of molding materials are uniformly mixed. The mixture M dispersed in the above is manufactured, and after a certain period of time, the slide damper 19 provided at the material discharge port 13a of the mixer 13 is opened to make one batch of the mixture M for one batch in the mixer 13. The charge hopper 20 supplies the charge hopper 20 with the charge hopper 20 temporarily storing the charge hopper 20.
Are sequentially supplied to the injection molding apparatus 1. However, the mixture M may be continuously supplied from the mixer 13.

The charge hopper 20 will be described. As shown in FIGS. 2 and 3, a substantially cylindrical transparent glass hopper main body 21 is provided, and the hopper main body 21 contains a mixture M for accommodating therein. A portion 22 is formed, flange portions 23 are formed at both upper and lower end portions of the hopper body 21, and the upper and lower flange portions 23 are connected by a plurality of reinforcing rods 24.
A capacitance level meter 25 is provided in the middle part of the reinforcing rod 24 of the book, and the hopper body 21 is oriented substantially vertically between the material discharge port 13a of the mixer 13 and the material supply port 1a of the injection molding apparatus 1. The upper end opening 26 of the hopper body 21 is configured to have the same diameter as the material discharge port 13a of the mixer 13 or a larger diameter than the material discharge port 13a.
The upper end opening 26 of the No. 1 is communicated with the material discharge port 13a of the mixer 13, and the lower end opening 27 of the hopper body 21 has the same diameter as the material supply port 1a of the injection molding apparatus 1 or the material supply port 1a.
The lower end opening 27 of the hopper body 21 communicates with the material supply port 1a of the injection molding apparatus 1. The hopper body 21 may be made of a material whose inner surface can be smoothly formed, and may be made of stainless steel, for example. A coating layer made of Teflon or the like having a small friction coefficient may be formed on the inner surface of the hopper body 21.

Next, the operation of the charge hopper 20 will be described while explaining the material supply method by the material supply device 10. First, in the weighing process, the load cell 17 is provided so that the three molding materials of the natural pellets, the recycled pellets, and the pigment master pellets respectively stored in the three storage tanks 15 of the four storage tanks 15 have a predetermined ratio. Is fed to the weighing hopper 16 while being sequentially weighed by one, and one batch (for example, 3
The molding material (kg) is stored in the weighing hopper 16.

Next, in the mixing step, the molding material contained in the weighing hopper 16 is pneumatically transported to the mixer 13
Then, the mixture is fed into the inside and the mixer 13 is operated for a certain period of time (for example, 30 seconds) to mix the three molding materials to obtain a uniformly dispersed mixture M. Next, in the feeding step, the material outlet 13a of the mixer 13 is moved by the slide damper 19.
Open, and charge one batch of Mixture M into Charge Hopper 2
0, and the mixture M is supplied from the material supply port 1a into the injection molding apparatus 1. Based on the signal from the level meter 25, the material of the charge hopper 20 becomes 1 or less each time A batch of Mixture M is fed. At this time, the mixture M supplied from the mixer 13 becomes a lump and falls freely and is accommodated in the hopper main body 21, so that the specific gravities and shapes of the three molding materials constituting the mixture M, Even if the physical properties such as size and surface roughness are different, the classification of the mixture M during the fall can be effectively prevented.

That is, since the inner surface of the hopper main body 21 is provided in a substantially vertical direction from the upper end to the lower end thereof, when the mixture M supplied from the mixer 13 into the charge hopper 20 falls freely. The frictional resistance between the mixture M and the inner peripheral surface of the charge hopper 20 can be minimized, and the mixture M can be aggregated and fall freely, so that the sliding contact between the mixtures M can be reduced. In addition, since the mixture M is unlikely to be chevron-shaped in the charge hopper 20, classification due to the difference in rolling friction is prevented, and since the hopper body 21 is made of glass, the inner surface of the hopper body 21 is made flat. It is possible to configure the structure, and the frictional resistance of the inner peripheral surface of the charge hopper 20 can be reduced. There is effectively prevented.

Further, if a coating layer made of Teflon or the like and having a small friction coefficient is formed on the inner surface of the hopper main body 21, the classification of the mixture M in the charge hopper 20 can be prevented more effectively. Further, if the hopper body 21 is made of transparent glass, it is possible to visually confirm the remaining amount of the mixture M contained in the hopper body 21.

Here, the results of the test conducted using the material supply device 10 will be described. 1500 round glass fiber-containing pellets (ash content: 40.3%) were used as the molding material.
g, 1470 g of natural round pellets, and 30 g of pigment master pellets (ash content: 30%) were weighed, mixed for 30 seconds by a paddle type mixer 13, and charged into a charge hopper 20.

The injection molding apparatus 1 has a standard screw head, a shutoff valve, and a nozzle diameter of 4φ15.
Using R, the molding conditions are a temperature of 230 ° C. and a mold 40.
℃, screw rotation speed 70 rpm, no back pressure, weighing 2
It was set to 10/495 mm, and the remaining amount was zero push molding.
As the mold, an A-3 mold 8 mm natural meat direct gate was used.

As a molding method, after purging before the nozzle for 5 shots, the 5 shot molded product is discarded, the molded product after that is sampled, and this molded product is used in Table 3 and FIG.
The test results shown in FIG. 5 were obtained. However, the logical value of ash of this molded product is 20.45%.

[0030]

[Table 3]

Further, instead of the round pellets containing glass fiber, columnar pellets containing glass fiber (length: 10 mm,
(Ash content: 42%) was used to sample the molded product in the same manner as described above, and the test results shown in Table 4 and FIGS. 4 and 5 were obtained using this molded product. However, the logical value of ash of this molded product is 2
It is 1.3%.

[0032]

[Table 4]

As can be seen from Tables 3 and 4, FIG. 4 and FIG. 5, the molded product was obtained even when the glass fiber-containing round pellets were used and also when the glass fiber-containing cylindrical pellets were used. It can be seen that variations in weight and ash content are almost unchanged, and deterioration of the quality of the molded product due to the shape of the pellet is prevented. Further, it can be seen that the variation in ash content is smaller than that in the case of using the conventional charge hopper (see Table 1), and the quality of the molded product is improved.

Next, a modification in which the structure of the charge hopper 20 is partially changed will be described. (1) In the hopper main body 21, the upper end opening 26 is set to be the same as the material discharge port 13a of the mixer 13 or set to a size surrounding the material discharge port 13a, and the lower end opening 27 is formed in the injection molding apparatus 1. The diameter of the material supply port 1a is the same as or smaller than that of the material supply port 1a, and the accommodation portion 22
If the angle formed by the inner surface of the side wall of the hopper main body 21 and the horizontal plane is set to 60 ° or more at an angle θ on the horizontal plane outside the side wall from the upper end to the lower end of the entire side wall. Alternatively, as shown in FIG. 6, a hopper body 21A that expands upward may be used, and as shown in FIG. 7, a hopper body 21B that expands downward may be used. Further, as shown in FIG. 8, an angle θ1 formed between the side walls facing each other and the horizontal plane,
The hopper body 21C in which θ2 is set to different angles may be used.

(2) The hopper bodies 21, 21A,
21B and 21C may be divided into upper and lower parts.
In addition, the hopper bodies 21, 21A, 21B, 21C
The cross section may be formed in a polygonal shape such as a square or a rectangle.

In this embodiment, the charge hopper 20 is used.
Although the mixture M supplied from the above was directly supplied to the injection molding apparatus 1, the mixture M supplied from the charge hopper 20 may be housed in a can or a box such as a drum can. Further, although the present invention is applied to the charge hopper 20 of the material supply device 10 of the injection molding device 1 in the present embodiment, it is arranged below the mixer for mixing granular or powdery medicines or foods. The present invention can be similarly applied to a charge hopper.

[0037]

According to the material supply method of the injection molding apparatus according to the first aspect of the present invention, the mixture and the charge are supplied when the mixture supplied from the mixer into the charge hopper falls freely and is supplied to the molding apparatus. Since the frictional resistance between the side walls of the hopper and the conical portion can be reduced, it is possible to effectively prevent classification of the mixture during the fall.

According to the charge hopper of the second aspect, at the time of free fall of the mixture supplied from the mixer into the charge hopper and at the time of supply to the molding device, between the side wall of the mixture and the charge hopper and the conical portion. Since the frictional resistance in can be reduced, the same effect as in claim 1 can be obtained.

According to the charge hopper of the third aspect, the side walls of the charge hopper are arranged in a substantially vertical direction, and the frictional resistance between the side walls of the mixture and the charge hopper and at the conical portion can be reduced as much as possible. And, it becomes possible to more effectively prevent the classification of the mixture during the supply to the molding apparatus. According to the charge hopper of the fourth aspect, since the side wall of the charge hopper is made of a transparent member, it is possible to visually confirm the remaining amount of the mixture with respect to the charge hopper.

According to the charge hopper of the fifth aspect, since the coating layer having a small friction coefficient is formed on the inner surface of the side wall of the charge hopper, the friction resistance between the mixture and the side wall of the charge hopper and at the conical portion is reduced. By further reducing the amount, it becomes possible to more effectively prevent the classification of the mixture during the dropping into the charge hopper and during the supply to the molding device. According to the charge hopper of claim 6, it becomes possible to reduce the frictional resistance between the mixture of a plurality of types of molding materials such as natural pellets, recycled pellets, glass fiber-containing pellets and the side wall of the charge hopper. It is possible to prevent the classification when the body is fed into the charge hopper and to manufacture a molded product of high quality.

According to the charge hopper of the seventh aspect, since the mixture is intermittently supplied from the mixture to the charge hopper in a constant amount, the constant amount of the mixture supplied from the mixer is made into one lump. It becomes possible to supply to the charge hopper, and it is possible to more effectively prevent classification of the mixture due to difference in rolling friction.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a material supply device

FIG. 2 is a side view of the mixer and the charge hopper.

[Fig. 3] Vertical sectional view of the hopper body

[Fig. 4] Diagram showing the ash content of the molded product

FIG. 5 is a diagram showing the weight of the molded product.

FIG. 6 is a vertical sectional view of a hopper body according to a first modification.

FIG. 7 is a vertical sectional view of a hopper body according to a second modification.

FIG. 8 is a vertical sectional view of a hopper body according to a third modification.

[Explanation of symbols]

M Mixer 20 Charge hopper 1 Injection molding device 21 Hopper body 1a Material supply port 22 Storage part 10 Material supply device 23 Flange part 11 Measuring part 24 Reinforcing rod 12 Mixing part 25 Level meter 13 Mixer 26 Upper end opening 13a Material discharge port 27 Lower end opening 14 Blower unit 21A Hopper body 15 Storage tank 21B Hopper body 16 Weighing hopper 21C Hopper body 16a Non-contact nozzle 17 Load cell 18 Slide damper 19 Slide damper

Claims (7)

[Claims] 1. A mixing step of mixing two or more types of injection molding materials having different physical properties such as specific gravity, shape, size and surface roughness with a mixer for a certain period of time to obtain a uniformly dispersed mixture. , The mixture in the mixer, the lower end opening has the same diameter as the material supply port of the injection molding device or smaller than the material supply port, and the upper end opening has the same diameter as the material discharge port of the mixer or the material discharge port. Also has a large diameter, and the angle between the inner surface of the side wall and the horizontal plane is
From the upper end to the lower end of the entire side wall, it is freely fallen and temporarily accommodated in the accommodating portion of the charge hopper set at an angle of 60 ° or more on the horizontal surface outside the side wall,
A material supplying method for an injection molding apparatus, comprising: a supply step of supplying the mixture housed in the charge hopper to an injection molding apparatus through a lower end opening thereof. 2. A mixture of two or more kinds of materials having different physical properties such as specific gravity, shape, size and surface roughness, which is connected to the material discharge port of the mixer and discharged from the mixer, is temporarily used. A charge hopper having an accommodating portion for accommodating, wherein the upper end opening of the charge hopper is set to the same size as the material discharge port of the mixer or a size surrounding the material discharge port,
In addition, the angle formed by the inner surface of the side wall forming the accommodating portion of the charge hopper and the horizontal plane is 60 ° at the angle on the horizontal plane outside the side wall from the upper end to the lower end of the entire side wall.
A charge hopper characterized by the above settings. 3. The charge hopper according to claim 2, wherein the side wall is arranged in a substantially vertical direction. 4. The charge hopper according to claim 2, wherein a side wall of the charge hopper is made of a transparent member. 5. The charge hopper according to claim 2, wherein a coating layer having a small friction coefficient is formed on an inner surface of a side wall of the charge hopper. 6. The mixture housed in the charge hopper is a mixture of molding materials, the lower end opening of the charge hopper is connected to the material supply port of the molding device, and the lower end opening of the charge hopper is connected to the molding device. The charge hopper according to any one of claims 2 to 5, wherein the charge hopper has the same diameter as the material supply port or a diameter smaller than the material supply port. 7. The charge hopper according to claim 2, wherein the mixture is intermittently supplied from the mixer to the charge hopper by a constant amount.